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 $246.89   5.458%   $260.3653   $260.37   $260.35   $260.40  
  Purchase #2 $212.86   12.564%   $239.6037   $239.60   $239.60   $239.60  
  Purchase #3 $43.57   9.218%   $47.5863   $47.59   $47.60   $47.60  
  Purchase #4 $214.47   9.109%   $234.0061   $234.01   $234.00   $234.00  
  Purchase #5 $167.71   6.531%   $178.6631   $178.66   $178.65   $178.70  
  Purchase #6 $112.29   10.761%   $124.3735   $124.37   $124.35   $124.40  
  Purchase #7 $184.28   3.613%   $190.938   $190.94   $190.95   $190.90  
  7 purchase totals = $1,182.07       $1,275.5360   $1,275.54   $1,275.50   $1,275.60