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 $176.53   3.507%   $182.7209   $182.72   $182.70   $182.70  
  Purchase #2 $33.79   13.686%   $38.4145   $38.41   $38.40   $38.40  
  Purchase #3 $175.89   13.663%   $199.9219   $199.92   $199.90   $199.90  
  Purchase #4 $96.79   6.157%   $102.7494   $102.75   $102.75   $102.70  
  Purchase #5 $67.25   8.644%   $73.0631   $73.06   $73.05   $73.10  
  Purchase #6 $233.91   7.485%   $251.4182   $251.42   $251.40   $251.40  
  Purchase #7 $240.56   10.272%   $265.2703   $265.27   $265.25   $265.30  
  7 purchase totals = $1,024.72       $1,113.5583   $1,113.55   $1,113.45   $1,113.50