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 $162.87   11.727%   $181.9698   $181.97   $181.95   $182.00  
  Purchase #2 $38.40   7.109%   $41.1299   $41.13   $41.15   $41.10  
  Purchase #3 $245.98   8.611%   $267.1613   $267.16   $267.15   $267.20  
  Purchase #4 $35.51   5.204%   $37.3579   $37.36   $37.35   $37.40  
  Purchase #5 $71.50   5.246%   $75.2509   $75.25   $75.25   $75.30  
  Purchase #6 $133.87   13.193%   $151.5315   $151.53   $151.55   $151.50  
  Purchase #7 $12.33   5.717%   $13.0349   $13.03   $13.05   $13.00  
  7 purchase totals = $700.46       $767.4362   $767.43   $767.45   $767.50