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 $218.80   12.256%   $245.6161   $245.62   $245.60   $245.60  
  Purchase #2 $226.52   4.565%   $236.8606   $236.86   $236.85   $236.90  
  Purchase #3 $55.66   6.430%   $59.2389   $59.24   $59.25   $59.20  
  Purchase #4 $210.32   7.327%   $225.7301   $225.73   $225.75   $225.70  
  Purchase #5 $60.67   4.242%   $63.2436   $63.24   $63.25   $63.20  
  Purchase #6 $165.60   13.302%   $187.6281   $187.63   $187.65   $187.60  
  Purchase #7 $193.79   13.678%   $220.2966   $220.30   $220.30   $220.30  
  7 purchase totals = $1,131.36       $1,238.6140   $1,238.62   $1,238.65   $1,238.50