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 $242.57   4.502%   $253.4905   $253.49   $253.50   $253.50  
  Purchase #2 $64.53   10.592%   $71.365   $71.37   $71.35   $71.40  
  Purchase #3 $119.55   11.800%   $133.6569   $133.66   $133.65   $133.70  
  Purchase #4 $53.76   5.649%   $56.7969   $56.80   $56.80   $56.80  
  Purchase #5 $110.77   6.425%   $117.887   $117.89   $117.90   $117.90  
  Purchase #6 $106.28   10.764%   $117.72   $117.72   $117.70   $117.70  
  Purchase #7 $173.33   12.561%   $195.102   $195.10   $195.10   $195.10  
  7 purchase totals = $870.79       $946.0183   $946.03   $946.00   $946.10