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 $246.87   8.362%   $267.5133   $267.51   $267.50   $267.50  
  Purchase #2 $13.53   8.409%   $14.6677   $14.67   $14.65   $14.70  
  Purchase #3 $250.73   6.452%   $266.9071   $266.91   $266.90   $266.90  
  Purchase #4 $222.31   10.808%   $246.3373   $246.34   $246.35   $246.30  
  Purchase #5 $90.33   5.766%   $95.5384   $95.54   $95.55   $95.50  
  Purchase #6 $106.93   5.674%   $112.9972   $113.00   $113.00   $113.00  
  Purchase #7 $240.25   12.734%   $270.8434   $270.84   $270.85   $270.80  
  7 purchase totals = $1,170.95       $1,274.8044   $1,274.81   $1,274.80   $1,274.70