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 $242.55   8.732%   $263.7295   $263.73   $263.75   $263.70  
  Purchase #2 $117.49   5.869%   $124.3855   $124.39   $124.40   $124.40  
  Purchase #3 $9.33   8.236%   $10.0984   $10.10   $10.10   $10.10  
  Purchase #4 $155.49   10.582%   $171.944   $171.94   $171.95   $171.90  
  Purchase #5 $214.67   5.390%   $226.2407   $226.24   $226.25   $226.20  
  Purchase #6 $75.82   11.845%   $84.8009   $84.80   $84.80   $84.80  
  Purchase #7 $71.59   4.487%   $74.8022   $74.80   $74.80   $74.80  
  7 purchase totals = $886.94       $956.0012   $956.00   $956.05   $955.90