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 $84.82   8.473%   $92.0068   $92.01   $92.00   $92.00  
  Purchase #2 $119.47   5.845%   $126.453   $126.45   $126.45   $126.50  
  Purchase #3 $124.54   3.474%   $128.8665   $128.87   $128.85   $128.90  
  Purchase #4 $65.74   6.282%   $69.8698   $69.87   $69.85   $69.90  
  Purchase #5 $56.82   6.108%   $60.2906   $60.29   $60.30   $60.30  
  Purchase #6 $190.46   5.347%   $200.6439   $200.64   $200.65   $200.60  
  Purchase #7 $223.81   4.243%   $233.3063   $233.31   $233.30   $233.30  
  7 purchase totals = $865.66       $911.4369   $911.44   $911.40   $911.50