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 $214.58   6.266%   $228.0256   $228.03   $228.05   $228.00  
  Purchase #2 $129.32   13.440%   $146.7006   $146.70   $146.70   $146.70  
  Purchase #3 $244.62   9.526%   $267.9225   $267.92   $267.90   $267.90  
  Purchase #4 $69.69   6.369%   $74.1286   $74.13   $74.15   $74.10  
  Purchase #5 $154.53   7.684%   $166.4041   $166.40   $166.40   $166.40  
  Purchase #6 $134.83   11.538%   $150.3867   $150.39   $150.40   $150.40  
  Purchase #7 $37.47   10.144%   $41.271   $41.27   $41.25   $41.30  
  7 purchase totals = $985.04       $1,074.8391   $1,074.84   $1,074.85   $1,074.80