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 $62.99   9.146%   $68.7511   $68.75   $68.75   $68.80  
  Purchase #2 $195.78   3.374%   $202.3856   $202.39   $202.40   $202.40  
  Purchase #3 $80.43   12.237%   $90.2722   $90.27   $90.25   $90.30  
  Purchase #4 $178.55   13.665%   $202.9489   $202.95   $202.95   $202.90  
  Purchase #5 $120.93   5.591%   $127.6912   $127.69   $127.70   $127.70  
  Purchase #6 $57.89   5.543%   $61.0988   $61.10   $61.10   $61.10  
  Purchase #7 $110.55   9.293%   $120.8234   $120.82   $120.80   $120.80  
  7 purchase totals = $807.12       $873.9712   $873.97   $873.95   $874.00