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 $56.95   8.113%   $61.5704   $61.57   $61.55   $61.60  
  Purchase #2 $112.88   3.358%   $116.6705   $116.67   $116.65   $116.70  
  Purchase #3 $123.54   6.709%   $131.8283   $131.83   $131.85   $131.80  
  Purchase #4 $88.42   10.673%   $97.8571   $97.86   $97.85   $97.90  
  Purchase #5 $116.77   13.811%   $132.8971   $132.90   $132.90   $132.90  
  Purchase #6 $41.60   6.347%   $44.2404   $44.24   $44.25   $44.20  
  Purchase #7 $236.81   5.580%   $250.024   $250.02   $250.00   $250.00  
  7 purchase totals = $776.97       $835.0878   $835.09   $835.05   $835.10