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 $63.59   6.271%   $67.5777   $67.58   $67.60   $67.60  
  Purchase #2 $204.50   13.507%   $232.1218   $232.12   $232.10   $232.10  
  Purchase #3 $244.44   6.724%   $260.8761   $260.88   $260.90   $260.90  
  Purchase #4 $34.78   10.747%   $38.5178   $38.52   $38.50   $38.50  
  Purchase #5 $245.75   6.641%   $262.0703   $262.07   $262.05   $262.10  
  Purchase #6 $28.54   7.739%   $30.7487   $30.75   $30.75   $30.70  
  Purchase #7 $188.66   6.279%   $200.506   $200.51   $200.50   $200.50  
  7 purchase totals = $1,010.26       $1,092.4184   $1,092.43   $1,092.40   $1,092.40