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 $33.59   11.825%   $37.562   $37.56   $37.55   $37.60  
  Purchase #2 $239.30   5.802%   $253.1842   $253.18   $253.20   $253.20  
  Purchase #3 $184.36   8.200%   $199.4775   $199.48   $199.50   $199.50  
  Purchase #4 $155.64   3.232%   $160.6703   $160.67   $160.65   $160.70  
  Purchase #5 $124.81   13.614%   $141.8016   $141.80   $141.80   $141.80  
  Purchase #6 $23.70   9.726%   $26.0051   $26.01   $26.00   $26.00  
  Purchase #7 $119.42   11.794%   $133.5044   $133.50   $133.50   $133.50  
  7 purchase totals = $880.82       $952.2051   $952.20   $952.20   $952.30