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 $8.66   7.793%   $9.3349   $9.33   $9.35   $9.30  
  Purchase #2 $177.52   12.289%   $199.3354   $199.34   $199.35   $199.30  
  Purchase #3 $88.87   13.233%   $100.6302   $100.63   $100.65   $100.60  
  Purchase #4 $61.95   6.129%   $65.7469   $65.75   $65.75   $65.70  
  Purchase #5 $244.48   3.617%   $253.3228   $253.32   $253.30   $253.30  
  Purchase #6 $117.93   9.367%   $128.9765   $128.98   $129.00   $129.00  
  Purchase #7 $37.30   7.535%   $40.1106   $40.11   $40.10   $40.10  
  7 purchase totals = $736.71       $797.4573   $797.46   $797.50   $797.30