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 $84.60   8.430%   $91.7318   $91.73   $91.75   $91.70  
  Purchase #2 $124.62   10.164%   $137.2864   $137.29   $137.30   $137.30  
  Purchase #3 $93.77   3.737%   $97.2742   $97.27   $97.25   $97.30  
  Purchase #4 $124.98   8.825%   $136.0095   $136.01   $136.00   $136.00  
  Purchase #5 $96.84   6.863%   $103.4861   $103.49   $103.50   $103.50  
  Purchase #6 $226.30   4.518%   $236.5242   $236.52   $236.50   $236.50  
  Purchase #7 $199.81   4.172%   $208.1461   $208.15   $208.15   $208.10  
  7 purchase totals = $950.92       $1,010.4583   $1,010.46   $1,010.45   $1,010.40