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 $240.93   7.611%   $259.2672   $259.27   $259.25   $259.30  
  Purchase #2 $102.80   8.118%   $111.1453   $111.15   $111.15   $111.10  
  Purchase #3 $176.76   9.621%   $193.7661   $193.77   $193.75   $193.80  
  Purchase #4 $92.48   5.102%   $97.1983   $97.20   $97.20   $97.20  
  Purchase #5 $93.66   9.475%   $102.5343   $102.53   $102.55   $102.50  
  Purchase #6 $56.95   3.165%   $58.7525   $58.75   $58.75   $58.80  
  Purchase #7 $199.49   6.313%   $212.0838   $212.08   $212.10   $212.10  
  7 purchase totals = $963.07       $1,034.7475   $1,034.75   $1,034.75   $1,034.80