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 $232.90   13.576%   $264.5185   $264.52   $264.50   $264.50  
  Purchase #2 $69.40   3.653%   $71.9352   $71.94   $71.95   $71.90  
  Purchase #3 $207.89   10.552%   $229.8266   $229.83   $229.85   $229.80  
  Purchase #4 $22.51   6.842%   $24.0501   $24.05   $24.05   $24.10  
  Purchase #5 $224.74   8.261%   $243.3058   $243.31   $243.30   $243.30  
  Purchase #6 $146.76   11.521%   $163.6682   $163.67   $163.65   $163.70  
  Purchase #7 $161.47   5.291%   $170.0134   $170.01   $170.00   $170.00  
  7 purchase totals = $1,065.67       $1,167.3178   $1,167.33   $1,167.30   $1,167.30