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 $194.26   11.505%   $216.6096   $216.61   $216.60   $216.60  
  Purchase #2 $148.51   3.507%   $153.7182   $153.72   $153.70   $153.70  
  Purchase #3 $20.45   7.254%   $21.9334   $21.93   $21.95   $21.90  
  Purchase #4 $204.99   4.620%   $214.4605   $214.46   $214.45   $214.50  
  Purchase #5 $50.50   6.402%   $53.733   $53.73   $53.75   $53.70  
  Purchase #6 $57.94   3.492%   $59.9633   $59.96   $59.95   $60.00  
  Purchase #7 $214.89   11.851%   $240.3566   $240.36   $240.35   $240.40  
  7 purchase totals = $891.54       $960.7746   $960.77   $960.75   $960.80