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 $244.73   8.141%   $264.6535   $264.65   $264.65   $264.70  
  Purchase #2 $236.90   13.429%   $268.7133   $268.71   $268.70   $268.70  
  Purchase #3 $140.87   9.619%   $154.4203   $154.42   $154.40   $154.40  
  Purchase #4 $101.31   4.691%   $106.0625   $106.06   $106.05   $106.10  
  Purchase #5 $167.58   6.586%   $178.6168   $178.62   $178.60   $178.60  
  Purchase #6 $93.31   4.551%   $97.5565   $97.56   $97.55   $97.60  
  Purchase #7 $95.53   13.282%   $108.2183   $108.22   $108.20   $108.20  
  7 purchase totals = $1,080.23       $1,178.2412   $1,178.24   $1,178.15   $1,178.30