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 $140.58   7.673%   $151.3667   $151.37   $151.35   $151.40  
  Purchase #2 $114.89   12.139%   $128.8365   $128.84   $128.85   $128.80  
  Purchase #3 $67.38   11.164%   $74.9023   $74.90   $74.90   $74.90  
  Purchase #4 $89.40   7.516%   $96.1193   $96.12   $96.10   $96.10  
  Purchase #5 $208.46   11.457%   $232.3433   $232.34   $232.35   $232.30  
  Purchase #6 $247.26   12.496%   $278.1576   $278.16   $278.15   $278.20  
  Purchase #7 $148.83   10.579%   $164.5747   $164.57   $164.55   $164.60  
  7 purchase totals = $1,016.80       $1,126.3004   $1,126.30   $1,126.25   $1,126.30