Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $170.65   13.862%   $194.3055   $194.31   $194.30   $194.30  
  Purchase #2 $124.45   4.194%   $129.6694   $129.67   $129.65   $129.70  
  Purchase #3 $178.81   13.524%   $202.9923   $202.99   $203.00   $203.00  
  Purchase #4 $170.90   4.606%   $178.7717   $178.77   $178.75   $178.80  
  Purchase #5 $166.80   8.305%   $180.6527   $180.65   $180.65   $180.70  
  Purchase #6 $164.75   11.311%   $183.3849   $183.38   $183.40   $183.40  
  Purchase #7 $235.43   10.592%   $260.3667   $260.37   $260.35   $260.40  
  7 purchase totals = $1,211.79       $1,330.1432   $1,330.14   $1,330.10   $1,330.30