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 $82.89   13.760%   $94.2957   $94.30   $94.30   $94.30  
  Purchase #2 $223.92   3.467%   $231.6833   $231.68   $231.70   $231.70  
  Purchase #3 $116.41   7.580%   $125.2339   $125.23   $125.25   $125.20  
  Purchase #4 $110.90   9.326%   $121.2425   $121.24   $121.25   $121.20  
  Purchase #5 $235.30   10.805%   $260.7242   $260.72   $260.70   $260.70  
  Purchase #6 $40.28   3.522%   $41.6987   $41.70   $41.70   $41.70  
  Purchase #7 $89.55   5.787%   $94.7323   $94.73   $94.75   $94.70  
  7 purchase totals = $899.25       $969.6106   $969.60   $969.65   $969.50