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 $54.88   7.761%   $59.1392   $59.14   $59.15   $59.10  
  Purchase #2 $238.43   13.450%   $270.4988   $270.50   $270.50   $270.50  
  Purchase #3 $246.62   3.323%   $254.8152   $254.82   $254.80   $254.80  
  Purchase #4 $59.77   8.593%   $64.906   $64.91   $64.90   $64.90  
  Purchase #5 $221.68   3.811%   $230.1282   $230.13   $230.15   $230.10  
  Purchase #6 $188.59   3.767%   $195.6942   $195.69   $195.70   $195.70  
  Purchase #7 $202.50   11.547%   $225.8827   $225.88   $225.90   $225.90  
  7 purchase totals = $1,212.47       $1,301.0643   $1,301.07   $1,301.10   $1,301.00