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 $54.84   10.641%   $60.6755   $60.68   $60.70   $60.70  
  Purchase #2 $92.56   3.436%   $95.7404   $95.74   $95.75   $95.70  
  Purchase #3 $231.82   11.639%   $258.8015   $258.80   $258.80   $258.80  
  Purchase #4 $130.92   5.441%   $138.0434   $138.04   $138.05   $138.00  
  Purchase #5 $43.72   9.246%   $47.7624   $47.76   $47.75   $47.80  
  Purchase #6 $44.94   7.564%   $48.3393   $48.34   $48.35   $48.30  
  Purchase #7 $233.61   13.729%   $265.6823   $265.68   $265.70   $265.70  
  7 purchase totals = $832.41       $915.0448   $915.04   $915.10   $915.00