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 $65.32   13.290%   $74.001   $74.00   $74.00   $74.00  
  Purchase #2 $125.64   12.730%   $141.634   $141.63   $141.65   $141.60  
  Purchase #3 $29.98   9.816%   $32.9228   $32.92   $32.90   $32.90  
  Purchase #4 $7.26   3.383%   $7.5056   $7.51   $7.50   $7.50  
  Purchase #5 $234.94   3.357%   $242.8269   $242.83   $242.85   $242.80  
  Purchase #6 $101.47   6.758%   $108.3273   $108.33   $108.35   $108.30  
  Purchase #7 $166.68   8.295%   $180.5061   $180.51   $180.50   $180.50  
  7 purchase totals = $731.29       $787.7237   $787.73   $787.75   $787.60