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 $189.48   7.248%   $203.2135   $203.21   $203.20   $203.20  
  Purchase #2 $125.77   12.851%   $141.9327   $141.93   $141.95   $141.90  
  Purchase #3 $229.90   5.846%   $243.34   $243.34   $243.35   $243.30  
  Purchase #4 $86.99   7.134%   $93.1959   $93.20   $93.20   $93.20  
  Purchase #5 $153.82   11.594%   $171.6539   $171.65   $171.65   $171.70  
  Purchase #6 $134.95   11.119%   $149.9551   $149.96   $149.95   $150.00  
  Purchase #7 $25.50   8.490%   $27.665   $27.67   $27.65   $27.70  
  7 purchase totals = $946.41       $1,030.9561   $1,030.96   $1,030.95   $1,031.00