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 $204.71   9.643%   $224.4502   $224.45   $224.45   $224.50  
  Purchase #2 $247.79   5.618%   $261.7108   $261.71   $261.70   $261.70  
  Purchase #3 $105.42   10.806%   $116.8117   $116.81   $116.80   $116.80  
  Purchase #4 $51.50   5.218%   $54.1873   $54.19   $54.20   $54.20  
  Purchase #5 $57.78   12.437%   $64.9661   $64.97   $64.95   $65.00  
  Purchase #6 $231.72   3.250%   $239.2509   $239.25   $239.25   $239.30  
  Purchase #7 $72.76   10.270%   $80.2325   $80.23   $80.25   $80.20  
  7 purchase totals = $971.68       $1,041.6095   $1,041.61   $1,041.60   $1,041.70