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 $125.44   5.590%   $132.4521   $132.45   $132.45   $132.50  
  Purchase #2 $59.85   5.257%   $62.9963   $63.00   $63.00   $63.00  
  Purchase #3 $188.37   8.450%   $204.2873   $204.29   $204.30   $204.30  
  Purchase #4 $207.35   11.489%   $231.1724   $231.17   $231.15   $231.20  
  Purchase #5 $148.53   7.767%   $160.0663   $160.07   $160.05   $160.10  
  Purchase #6 $19.29   4.383%   $20.1355   $20.14   $20.15   $20.10  
  Purchase #7 $194.93   3.374%   $201.5069   $201.51   $201.50   $201.50  
  7 purchase totals = $943.76       $1,012.6168   $1,012.63   $1,012.60   $1,012.70