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 $224.96   11.859%   $251.638   $251.64   $251.65   $251.60  
  Purchase #2 $87.58   7.804%   $94.4147   $94.41   $94.40   $94.40  
  Purchase #3 $71.49   13.793%   $81.3506   $81.35   $81.35   $81.40  
  Purchase #4 $230.38   6.217%   $244.7027   $244.70   $244.70   $244.70  
  Purchase #5 $80.70   12.458%   $90.7536   $90.75   $90.75   $90.80  
  Purchase #6 $131.84   5.313%   $138.8447   $138.84   $138.85   $138.80  
  Purchase #7 $136.50   6.338%   $145.1514   $145.15   $145.15   $145.20  
  7 purchase totals = $963.45       $1,046.8557   $1,046.84   $1,046.85   $1,046.90