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 $42.45   5.447%   $44.7623   $44.76   $44.75   $44.80  
  Purchase #2 $236.48   4.111%   $246.2017   $246.20   $246.20   $246.20  
  Purchase #3 $108.92   11.805%   $121.778   $121.78   $121.80   $121.80  
  Purchase #4 $139.41   11.315%   $155.1842   $155.18   $155.20   $155.20  
  Purchase #5 $133.84   7.145%   $143.4029   $143.40   $143.40   $143.40  
  Purchase #6 $188.41   6.583%   $200.813   $200.81   $200.80   $200.80  
  Purchase #7 $91.73   11.217%   $102.0194   $102.02   $102.00   $102.00  
  7 purchase totals = $941.24       $1,014.1615   $1,014.15   $1,014.15   $1,014.20