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 $54.36   13.638%   $61.7736   $61.77   $61.75   $61.80  
  Purchase #2 $156.42   7.379%   $167.9622   $167.96   $167.95   $168.00  
  Purchase #3 $57.49   8.445%   $62.345   $62.35   $62.35   $62.30  
  Purchase #4 $206.77   8.457%   $224.2565   $224.26   $224.25   $224.30  
  Purchase #5 $113.95   6.413%   $121.2576   $121.26   $121.25   $121.30  
  Purchase #6 $156.95   7.168%   $168.2002   $168.20   $168.20   $168.20  
  Purchase #7 $168.73   12.687%   $190.1368   $190.14   $190.15   $190.10  
  7 purchase totals = $914.67       $995.9319   $995.94   $995.90   $996.00