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 $208.34   13.511%   $236.4888   $236.49   $236.50   $236.50  
  Purchase #2 $144.54   8.728%   $157.1555   $157.16   $157.15   $157.20  
  Purchase #3 $156.68   5.736%   $165.6672   $165.67   $165.65   $165.70  
  Purchase #4 $46.84   9.843%   $51.4505   $51.45   $51.45   $51.50  
  Purchase #5 $218.25   5.224%   $229.6514   $229.65   $229.65   $229.70  
  Purchase #6 $149.29   3.310%   $154.2315   $154.23   $154.25   $154.20  
  Purchase #7 $31.70   12.250%   $35.5833   $35.58   $35.60   $35.60  
  7 purchase totals = $955.64       $1,030.2282   $1,030.23   $1,030.25   $1,030.40