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 $134.39   8.463%   $145.7634   $145.76   $145.75   $145.80  
  Purchase #2 $70.70   6.467%   $75.2722   $75.27   $75.25   $75.30  
  Purchase #3 $207.72   9.193%   $226.8157   $226.82   $226.80   $226.80  
  Purchase #4 $203.66   10.243%   $224.5209   $224.52   $224.50   $224.50  
  Purchase #5 $125.69   10.844%   $139.3198   $139.32   $139.30   $139.30  
  Purchase #6 $85.90   11.709%   $95.958   $95.96   $95.95   $96.00  
  Purchase #7 $46.45   5.141%   $48.838   $48.84   $48.85   $48.80  
  7 purchase totals = $874.51       $956.4880   $956.49   $956.40   $956.50