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 $202.64   11.417%   $225.7754   $225.78   $225.80   $225.80  
  Purchase #2 $49.71   7.400%   $53.3885   $53.39   $53.40   $53.40  
  Purchase #3 $60.28   6.622%   $64.2717   $64.27   $64.25   $64.30  
  Purchase #4 $233.92   5.846%   $247.595   $247.60   $247.60   $247.60  
  Purchase #5 $195.55   11.303%   $217.653   $217.65   $217.65   $217.70  
  Purchase #6 $160.75   11.216%   $178.7797   $178.78   $178.80   $178.80  
  Purchase #7 $207.58   13.297%   $235.1819   $235.18   $235.20   $235.20  
  7 purchase totals = $1,110.43       $1,222.6452   $1,222.65   $1,222.70   $1,222.80