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 $86.33   9.398%   $94.4433   $94.44   $94.45   $94.40  
  Purchase #2 $55.26   13.390%   $62.6593   $62.66   $62.65   $62.70  
  Purchase #3 $20.83   6.489%   $22.1817   $22.18   $22.20   $22.20  
  Purchase #4 $207.73   6.701%   $221.65   $221.65   $221.65   $221.70  
  Purchase #5 $229.97   3.693%   $238.4628   $238.46   $238.45   $238.50  
  Purchase #6 $241.29   3.470%   $249.6628   $249.66   $249.65   $249.70  
  Purchase #7 $17.87   11.850%   $19.9876   $19.99   $20.00   $20.00  
  7 purchase totals = $859.28       $909.0475   $909.04   $909.05   $909.20