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 $64.76   5.497%   $68.3199   $68.32   $68.30   $68.30  
  Purchase #2 $118.79   6.839%   $126.914   $126.91   $126.90   $126.90  
  Purchase #3 $105.74   8.344%   $114.5629   $114.56   $114.55   $114.60  
  Purchase #4 $174.89   13.503%   $198.5054   $198.51   $198.50   $198.50  
  Purchase #5 $181.78   5.802%   $192.3269   $192.33   $192.35   $192.30  
  Purchase #6 $38.57   12.697%   $43.4672   $43.47   $43.45   $43.50  
  Purchase #7 $119.63   11.309%   $133.159   $133.16   $133.15   $133.20  
  7 purchase totals = $804.16       $877.2553   $877.26   $877.20   $877.30