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 $94.53   4.554%   $98.8349   $98.83   $98.85   $98.80  
  Purchase #2 $211.28   4.206%   $220.1664   $220.17   $220.15   $220.20  
  Purchase #3 $11.27   3.373%   $11.6501   $11.65   $11.65   $11.70  
  Purchase #4 $177.86   11.235%   $197.8426   $197.84   $197.85   $197.80  
  Purchase #5 $250.35   9.782%   $274.8392   $274.84   $274.85   $274.80  
  Purchase #6 $104.67   12.527%   $117.782   $117.78   $117.80   $117.80  
  Purchase #7 $82.56   11.463%   $92.0239   $92.02   $92.00   $92.00  
  7 purchase totals = $932.52       $1,013.1391   $1,013.13   $1,013.15   $1,013.10