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 $249.48   5.268%   $262.6226   $262.62   $262.60   $262.60  
  Purchase #2 $159.71   9.738%   $175.2626   $175.26   $175.25   $175.30  
  Purchase #3 $238.97   7.829%   $257.679   $257.68   $257.70   $257.70  
  Purchase #4 $85.32   8.672%   $92.719   $92.72   $92.70   $92.70  
  Purchase #5 $177.52   9.345%   $194.1092   $194.11   $194.10   $194.10  
  Purchase #6 $213.28   11.230%   $237.2313   $237.23   $237.25   $237.20  
  Purchase #7 $49.73   9.746%   $54.5767   $54.58   $54.60   $54.60  
  7 purchase totals = $1,174.01       $1,274.2004   $1,274.20   $1,274.20   $1,274.20