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 $89.38   8.554%   $97.0256   $97.03   $97.05   $97.00  
  Purchase #2 $35.96   9.411%   $39.3442   $39.34   $39.35   $39.30  
  Purchase #3 $146.68   3.777%   $152.2201   $152.22   $152.20   $152.20  
  Purchase #4 $223.87   6.309%   $237.994   $237.99   $238.00   $238.00  
  Purchase #5 $205.80   5.285%   $216.6765   $216.68   $216.70   $216.70  
  Purchase #6 $137.90   13.465%   $156.4682   $156.47   $156.45   $156.50  
  Purchase #7 $224.42   12.531%   $252.5421   $252.54   $252.55   $252.50  
  7 purchase totals = $1,064.01       $1,152.2707   $1,152.27   $1,152.30   $1,152.20