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 $91.86   4.785%   $96.2555   $96.26   $96.25   $96.30  
  Purchase #2 $61.37   11.693%   $68.546   $68.55   $68.55   $68.50  
  Purchase #3 $224.72   12.537%   $252.8931   $252.89   $252.90   $252.90  
  Purchase #4 $21.88   7.163%   $23.4473   $23.45   $23.45   $23.40  
  Purchase #5 $180.85   8.268%   $195.8027   $195.80   $195.80   $195.80  
  Purchase #6 $146.66   7.410%   $157.5275   $157.53   $157.55   $157.50  
  Purchase #7 $154.55   6.224%   $164.1692   $164.17   $164.15   $164.20  
  7 purchase totals = $881.89       $958.6413   $958.65   $958.65   $958.60