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 $33.39   3.757%   $34.6445   $34.64   $34.65   $34.60  
  Purchase #2 $131.92   6.464%   $140.4473   $140.45   $140.45   $140.40  
  Purchase #3 $205.73   5.126%   $216.2757   $216.28   $216.30   $216.30  
  Purchase #4 $245.40   6.264%   $260.7719   $260.77   $260.75   $260.80  
  Purchase #5 $204.33   10.133%   $225.0348   $225.03   $225.05   $225.00  
  Purchase #6 $210.40   12.353%   $236.3907   $236.39   $236.40   $236.40  
  Purchase #7 $201.54   6.636%   $214.9142   $214.91   $214.90   $214.90  
  7 purchase totals = $1,232.71       $1,328.4791   $1,328.47   $1,328.50   $1,328.40