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 $82.77   11.541%   $92.3225   $92.32   $92.30   $92.30  
  Purchase #2 $245.82   11.501%   $274.0918   $274.09   $274.10   $274.10  
  Purchase #3 $248.26   3.404%   $256.7108   $256.71   $256.70   $256.70  
  Purchase #4 $136.34   10.363%   $150.4689   $150.47   $150.45   $150.50  
  Purchase #5 $179.35   9.812%   $196.9478   $196.95   $196.95   $196.90  
  Purchase #6 $247.53   8.135%   $267.6666   $267.67   $267.65   $267.70  
  Purchase #7 $229.54   3.372%   $237.2801   $237.28   $237.30   $237.30  
  7 purchase totals = $1,369.61       $1,475.4885   $1,475.49   $1,475.45   $1,475.50