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 $61.26   5.350%   $64.5374   $64.54   $64.55   $64.50  
  Purchase #2 $125.98   4.759%   $131.9754   $131.98   $132.00   $132.00  
  Purchase #3 $247.47   4.636%   $258.9427   $258.94   $258.95   $258.90  
  Purchase #4 $215.76   13.793%   $245.5198   $245.52   $245.50   $245.50  
  Purchase #5 $70.75   5.567%   $74.6887   $74.69   $74.70   $74.70  
  Purchase #6 $13.84   6.704%   $14.7678   $14.77   $14.75   $14.80  
  Purchase #7 $50.41   9.718%   $55.3088   $55.31   $55.30   $55.30  
  7 purchase totals = $785.47       $845.7406   $845.75   $845.75   $845.70