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 $103.42   10.607%   $114.3898   $114.39   $114.40   $114.40  
  Purchase #2 $206.37   10.788%   $228.6332   $228.63   $228.65   $228.60  
  Purchase #3 $148.41   13.843%   $168.9544   $168.95   $168.95   $169.00  
  Purchase #4 $61.34   11.794%   $68.5744   $68.57   $68.55   $68.60  
  Purchase #5 $116.34   8.771%   $126.5442   $126.54   $126.55   $126.50  
  Purchase #6 $129.76   9.863%   $142.5582   $142.56   $142.55   $142.60  
  Purchase #7 $192.26   6.187%   $204.1551   $204.16   $204.15   $204.20  
  7 purchase totals = $957.90       $1,053.8093   $1,053.80   $1,053.80   $1,053.90