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 $60.83   4.853%   $63.7821   $63.78   $63.80   $63.80  
  Purchase #2 $244.81   10.172%   $269.7121   $269.71   $269.70   $269.70  
  Purchase #3 $85.71   4.365%   $89.4512   $89.45   $89.45   $89.50  
  Purchase #4 $125.65   8.431%   $136.2436   $136.24   $136.25   $136.20  
  Purchase #5 $36.44   7.580%   $39.2022   $39.20   $39.20   $39.20  
  Purchase #6 $238.62   10.838%   $264.4816   $264.48   $264.50   $264.50  
  Purchase #7 $232.96   12.169%   $261.3089   $261.31   $261.30   $261.30  
  7 purchase totals = $1,025.02       $1,124.1817   $1,124.17   $1,124.20   $1,124.20