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 $169.27   9.662%   $185.6249   $185.62   $185.60   $185.60  
  Purchase #2 $134.25   5.595%   $141.7613   $141.76   $141.75   $141.80  
  Purchase #3 $218.80   13.824%   $249.0469   $249.05   $249.05   $249.00  
  Purchase #4 $250.43   6.827%   $267.5269   $267.53   $267.55   $267.50  
  Purchase #5 $188.42   6.363%   $200.4092   $200.41   $200.40   $200.40  
  Purchase #6 $125.25   8.167%   $135.4792   $135.48   $135.50   $135.50  
  Purchase #7 $77.76   8.739%   $84.5554   $84.56   $84.55   $84.60  
  7 purchase totals = $1,164.18       $1,264.4038   $1,264.41   $1,264.40   $1,264.40