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 $59.68   4.293%   $62.2421   $62.24   $62.25   $62.20  
  Purchase #2 $105.34   9.861%   $115.7276   $115.73   $115.75   $115.70  
  Purchase #3 $158.63   4.368%   $165.559   $165.56   $165.55   $165.60  
  Purchase #4 $18.79   4.719%   $19.6767   $19.68   $19.70   $19.70  
  Purchase #5 $125.73   7.402%   $135.0365   $135.04   $135.05   $135.00  
  Purchase #6 $243.51   11.418%   $271.314   $271.31   $271.30   $271.30  
  Purchase #7 $37.94   3.194%   $39.1518   $39.15   $39.15   $39.20  
  7 purchase totals = $749.62       $808.7077   $808.71   $808.75   $808.70