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 $167.69   9.852%   $184.2108   $184.21   $184.20   $184.20  
  Purchase #2 $59.27   5.805%   $62.7106   $62.71   $62.70   $62.70  
  Purchase #3 $68.78   7.319%   $73.814   $73.81   $73.80   $73.80  
  Purchase #4 $19.88   12.356%   $22.3364   $22.34   $22.35   $22.30  
  Purchase #5 $137.50   13.842%   $156.5328   $156.53   $156.55   $156.50  
  Purchase #6 $86.92   8.645%   $94.4342   $94.43   $94.45   $94.40  
  Purchase #7 $188.59   7.634%   $202.987   $202.99   $203.00   $203.00  
  7 purchase totals = $728.63       $797.0258   $797.02   $797.05   $796.90