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 $10.84   5.852%   $11.4744   $11.47   $11.45   $11.50  
  Purchase #2 $68.90   11.741%   $76.9895   $76.99   $77.00   $77.00  
  Purchase #3 $54.62   8.450%   $59.2354   $59.24   $59.25   $59.20  
  Purchase #4 $96.95   7.635%   $104.3521   $104.35   $104.35   $104.40  
  Purchase #5 $208.86   11.534%   $232.9499   $232.95   $232.95   $232.90  
  Purchase #6 $167.92   5.227%   $176.6972   $176.70   $176.70   $176.70  
  Purchase #7 $228.81   4.780%   $239.7471   $239.75   $239.75   $239.70  
  7 purchase totals = $836.90       $901.4456   $901.45   $901.45   $901.40