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 $46.78   3.122%   $48.2405   $48.24   $48.25   $48.20  
  Purchase #2 $167.94   5.342%   $176.9114   $176.91   $176.90   $176.90  
  Purchase #3 $59.71   3.573%   $61.8434   $61.84   $61.85   $61.80  
  Purchase #4 $41.82   6.332%   $44.468   $44.47   $44.45   $44.50  
  Purchase #5 $148.59   8.158%   $160.712   $160.71   $160.70   $160.70  
  Purchase #6 $165.96   9.422%   $181.5968   $181.60   $181.60   $181.60  
  Purchase #7 $195.42   6.560%   $208.2396   $208.24   $208.25   $208.20  
  7 purchase totals = $826.22       $882.0117   $882.01   $882.00   $881.90