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 $114.38   10.666%   $126.5798   $126.58   $126.60   $126.60  
  Purchase #2 $202.74   13.836%   $230.7911   $230.79   $230.80   $230.80  
  Purchase #3 $149.42   3.218%   $154.2283   $154.23   $154.25   $154.20  
  Purchase #4 $199.67   5.789%   $211.2289   $211.23   $211.25   $211.20  
  Purchase #5 $145.75   5.852%   $154.2793   $154.28   $154.30   $154.30  
  Purchase #6 $249.65   13.234%   $282.6887   $282.69   $282.70   $282.70  
  Purchase #7 $125.74   11.842%   $140.6301   $140.63   $140.65   $140.60  
  7 purchase totals = $1,187.35       $1,300.4262   $1,300.43   $1,300.55   $1,300.40