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 $67.62   12.807%   $76.2801   $76.28   $76.30   $76.30  
  Purchase #2 $129.84   6.583%   $138.3874   $138.39   $138.40   $138.40  
  Purchase #3 $141.47   10.833%   $156.7954   $156.80   $156.80   $156.80  
  Purchase #4 $223.92   4.581%   $234.1778   $234.18   $234.20   $234.20  
  Purchase #5 $20.51   13.716%   $23.3232   $23.32   $23.30   $23.30  
  Purchase #6 $170.63   4.173%   $177.7504   $177.75   $177.75   $177.80  
  Purchase #7 $133.76   10.364%   $147.6229   $147.62   $147.60   $147.60  
  7 purchase totals = $887.75       $954.3372   $954.34   $954.35   $954.40