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 $59.98   5.775%   $63.4438   $63.44   $63.45   $63.40  
  Purchase #2 $145.99   3.799%   $151.5362   $151.54   $151.55   $151.50  
  Purchase #3 $106.47   6.522%   $113.414   $113.41   $113.40   $113.40  
  Purchase #4 $149.45   10.398%   $164.9898   $164.99   $165.00   $165.00  
  Purchase #5 $54.72   5.752%   $57.8675   $57.87   $57.85   $57.90  
  Purchase #6 $89.74   7.607%   $96.5665   $96.57   $96.55   $96.60  
  Purchase #7 $165.99   5.188%   $174.6016   $174.60   $174.60   $174.60  
  7 purchase totals = $772.34       $822.4194   $822.42   $822.40   $822.40