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 $53.63   10.283%   $59.1448   $59.14   $59.15   $59.10  
  Purchase #2 $236.99   13.161%   $268.1803   $268.18   $268.20   $268.20  
  Purchase #3 $79.33   10.642%   $87.7723   $87.77   $87.75   $87.80  
  Purchase #4 $237.52   12.123%   $266.3145   $266.31   $266.30   $266.30  
  Purchase #5 $241.73   12.503%   $271.9535   $271.95   $271.95   $272.00  
  Purchase #6 $125.87   13.819%   $143.264   $143.26   $143.25   $143.30  
  Purchase #7 $81.50   13.224%   $92.2776   $92.28   $92.30   $92.30  
  7 purchase totals = $1,056.57       $1,188.9070   $1,188.89   $1,188.90   $1,189.00