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 $109.84   12.239%   $123.2833   $123.28   $123.30   $123.30  
  Purchase #2 $103.93   8.864%   $113.1424   $113.14   $113.15   $113.10  
  Purchase #3 $48.59   11.551%   $54.2026   $54.20   $54.20   $54.20  
  Purchase #4 $224.44   8.245%   $242.9451   $242.95   $242.95   $242.90  
  Purchase #5 $196.54   13.117%   $222.3202   $222.32   $222.30   $222.30  
  Purchase #6 $123.41   9.432%   $135.05   $135.05   $135.05   $135.10  
  Purchase #7 $22.27   11.324%   $24.7919   $24.79   $24.80   $24.80  
  7 purchase totals = $829.02       $915.7355   $915.73   $915.75   $915.70