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 $101.89   5.127%   $107.1139   $107.11   $107.10   $107.10  
  Purchase #2 $74.31   5.462%   $78.3688   $78.37   $78.35   $78.40  
  Purchase #3 $228.92   9.809%   $251.3748   $251.37   $251.35   $251.40  
  Purchase #4 $53.54   13.172%   $60.5923   $60.59   $60.60   $60.60  
  Purchase #5 $75.26   5.530%   $79.4219   $79.42   $79.40   $79.40  
  Purchase #6 $200.45   11.372%   $223.2452   $223.25   $223.25   $223.20  
  Purchase #7 $190.43   7.199%   $204.1391   $204.14   $204.15   $204.10  
  7 purchase totals = $924.80       $1,004.2560   $1,004.25   $1,004.20   $1,004.20