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 $225.26   11.117%   $250.3022   $250.30   $250.30   $250.30  
  Purchase #2 $11.78   8.121%   $12.7367   $12.74   $12.75   $12.70  
  Purchase #3 $131.79   7.563%   $141.7573   $141.76   $141.75   $141.80  
  Purchase #4 $174.84   9.128%   $190.7994   $190.80   $190.80   $190.80  
  Purchase #5 $141.76   5.385%   $149.3938   $149.39   $149.40   $149.40  
  Purchase #6 $120.67   13.118%   $136.4995   $136.50   $136.50   $136.50  
  Purchase #7 $120.25   8.846%   $130.8873   $130.89   $130.90   $130.90  
  7 purchase totals = $926.35       $1,012.3762   $1,012.38   $1,012.40   $1,012.40