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 $84.25   11.722%   $94.1258   $94.13   $94.15   $94.10  
  Purchase #2 $242.30   6.378%   $257.7539   $257.75   $257.75   $257.80  
  Purchase #3 $175.45   10.388%   $193.6757   $193.68   $193.70   $193.70  
  Purchase #4 $62.65   11.163%   $69.6436   $69.64   $69.65   $69.60  
  Purchase #5 $157.73   6.308%   $167.6796   $167.68   $167.70   $167.70  
  Purchase #6 $139.52   13.688%   $158.6175   $158.62   $158.60   $158.60  
  Purchase #7 $31.81   8.864%   $34.6296   $34.63   $34.65   $34.60  
  7 purchase totals = $893.71       $976.1257   $976.13   $976.20   $976.10