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 $194.59   9.380%   $212.8425   $212.84   $212.85   $212.80  
  Purchase #2 $11.59   4.635%   $12.1272   $12.13   $12.15   $12.10  
  Purchase #3 $77.34   5.716%   $81.7608   $81.76   $81.75   $81.80  
  Purchase #4 $51.71   9.489%   $56.6168   $56.62   $56.60   $56.60  
  Purchase #5 $237.61   10.697%   $263.0271   $263.03   $263.05   $263.00  
  Purchase #6 $76.75   5.368%   $80.8699   $80.87   $80.85   $80.90  
  Purchase #7 $214.84   3.342%   $222.02   $222.02   $222.00   $222.00  
  7 purchase totals = $864.43       $929.2643   $929.27   $929.25   $929.20