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 $148.87   12.121%   $166.9145   $166.91   $166.90   $166.90  
  Purchase #2 $212.36   7.154%   $227.5522   $227.55   $227.55   $227.60  
  Purchase #3 $59.30   13.263%   $67.165   $67.17   $67.15   $67.20  
  Purchase #4 $125.61   10.782%   $139.1533   $139.15   $139.15   $139.20  
  Purchase #5 $244.90   10.587%   $270.8276   $270.83   $270.85   $270.80  
  Purchase #6 $175.26   5.318%   $184.5803   $184.58   $184.60   $184.60  
  Purchase #7 $68.95   4.450%   $72.0183   $72.02   $72.00   $72.00  
  7 purchase totals = $1,035.25       $1,128.2112   $1,128.21   $1,128.20   $1,128.30