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 $248.34   11.355%   $276.539   $276.54   $276.55   $276.50  
  Purchase #2 $161.37   12.707%   $181.8753   $181.88   $181.90   $181.90  
  Purchase #3 $97.61   5.153%   $102.6398   $102.64   $102.65   $102.60  
  Purchase #4 $174.71   3.635%   $181.0607   $181.06   $181.05   $181.10  
  Purchase #5 $74.71   12.731%   $84.2213   $84.22   $84.20   $84.20  
  Purchase #6 $92.94   9.411%   $101.6866   $101.69   $101.70   $101.70  
  Purchase #7 $12.44   6.738%   $13.2782   $13.28   $13.30   $13.30  
  7 purchase totals = $862.12       $941.3009   $941.31   $941.35   $941.30