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 $21.96   9.560%   $24.0594   $24.06   $24.05   $24.10  
  Purchase #2 $213.62   8.462%   $231.6965   $231.70   $231.70   $231.70  
  Purchase #3 $214.78   5.173%   $225.8906   $225.89   $225.90   $225.90  
  Purchase #4 $97.82   6.377%   $104.058   $104.06   $104.05   $104.10  
  Purchase #5 $109.64   12.671%   $123.5325   $123.53   $123.55   $123.50  
  Purchase #6 $126.55   7.562%   $136.1197   $136.12   $136.10   $136.10  
  Purchase #7 $15.94   5.610%   $16.8342   $16.83   $16.85   $16.80  
  7 purchase totals = $800.31       $862.1909   $862.19   $862.20   $862.20