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 $74.93   3.114%   $77.2633   $77.26   $77.25   $77.30  
  Purchase #2 $208.28   12.278%   $233.8526   $233.85   $233.85   $233.90  
  Purchase #3 $218.72   4.682%   $228.9605   $228.96   $228.95   $229.00  
  Purchase #4 $142.82   4.821%   $149.7054   $149.71   $149.70   $149.70  
  Purchase #5 $132.27   8.137%   $143.0328   $143.03   $143.05   $143.00  
  Purchase #6 $42.39   10.722%   $46.9351   $46.94   $46.95   $46.90  
  Purchase #7 $165.79   11.691%   $185.1725   $185.17   $185.15   $185.20  
  7 purchase totals = $985.20       $1,064.9222   $1,064.92   $1,064.90   $1,065.00