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 $191.32   13.109%   $216.4001   $216.40   $216.40   $216.40  
  Purchase #2 $99.95   10.642%   $110.5867   $110.59   $110.60   $110.60  
  Purchase #3 $68.37   11.862%   $76.48   $76.48   $76.50   $76.50  
  Purchase #4 $84.75   6.367%   $90.146   $90.15   $90.15   $90.10  
  Purchase #5 $206.95   8.774%   $225.1078   $225.11   $225.10   $225.10  
  Purchase #6 $78.81   10.702%   $87.2442   $87.24   $87.25   $87.20  
  Purchase #7 $196.39   5.595%   $207.378   $207.38   $207.40   $207.40  
  7 purchase totals = $926.54       $1,013.3428   $1,013.35   $1,013.40   $1,013.30