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 $99.85   9.539%   $109.3747   $109.37   $109.35   $109.40  
  Purchase #2 $81.76   5.790%   $86.4939   $86.49   $86.50   $86.50  
  Purchase #3 $223.96   9.154%   $244.4613   $244.46   $244.45   $244.50  
  Purchase #4 $155.59   3.287%   $160.7042   $160.70   $160.70   $160.70  
  Purchase #5 $44.60   9.870%   $49.002   $49.00   $49.00   $49.00  
  Purchase #6 $111.53   12.361%   $125.3162   $125.32   $125.30   $125.30  
  Purchase #7 $85.98   10.679%   $95.1618   $95.16   $95.15   $95.20  
  7 purchase totals = $803.27       $870.5141   $870.50   $870.45   $870.60