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 $234.55   12.147%   $263.0408   $263.04   $263.05   $263.00  
  Purchase #2 $220.57   6.366%   $234.6115   $234.61   $234.60   $234.60  
  Purchase #3 $53.76   6.700%   $57.3619   $57.36   $57.35   $57.40  
  Purchase #4 $47.26   4.102%   $49.1986   $49.20   $49.20   $49.20  
  Purchase #5 $180.43   9.185%   $197.0025   $197.00   $197.00   $197.00  
  Purchase #6 $72.88   13.468%   $82.6955   $82.70   $82.70   $82.70  
  Purchase #7 $125.38   5.260%   $131.975   $131.98   $132.00   $132.00  
  7 purchase totals = $934.83       $1,015.8858   $1,015.89   $1,015.90   $1,015.90