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 $231.83   12.596%   $261.0313   $261.03   $261.05   $261.00  
  Purchase #2 $188.72   13.255%   $213.7348   $213.73   $213.75   $213.70  
  Purchase #3 $218.72   8.472%   $237.25   $237.25   $237.25   $237.30  
  Purchase #4 $54.75   3.553%   $56.6953   $56.70   $56.70   $56.70  
  Purchase #5 $96.95   13.770%   $110.3   $110.30   $110.30   $110.30  
  Purchase #6 $31.75   9.700%   $34.8298   $34.83   $34.85   $34.80  
  Purchase #7 $25.33   12.272%   $28.4385   $28.44   $28.45   $28.40  
  7 purchase totals = $848.05       $942.2797   $942.28   $942.35   $942.20