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 $82.59   12.151%   $92.6255   $92.63   $92.65   $92.60  
  Purchase #2 $209.87   7.175%   $224.9282   $224.93   $224.95   $224.90  
  Purchase #3 $141.55   4.490%   $147.9056   $147.91   $147.90   $147.90  
  Purchase #4 $191.82   8.384%   $207.9022   $207.90   $207.90   $207.90  
  Purchase #5 $33.47   13.805%   $38.0905   $38.09   $38.10   $38.10  
  Purchase #6 $157.50   12.331%   $176.9213   $176.92   $176.90   $176.90  
  Purchase #7 $43.99   3.334%   $45.4566   $45.46   $45.45   $45.50  
  7 purchase totals = $860.79       $933.8299   $933.84   $933.85   $933.80