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 $24.77   3.170%   $25.5552   $25.56   $25.55   $25.60  
  Purchase #2 $194.99   12.831%   $220.0092   $220.01   $220.00   $220.00  
  Purchase #3 $185.44   5.404%   $195.4612   $195.46   $195.45   $195.50  
  Purchase #4 $242.91   8.210%   $262.8529   $262.85   $262.85   $262.90  
  Purchase #5 $33.51   4.847%   $35.1342   $35.13   $35.15   $35.10  
  Purchase #6 $36.34   6.702%   $38.7755   $38.78   $38.80   $38.80  
  Purchase #7 $174.82   3.330%   $180.6415   $180.64   $180.65   $180.60  
  7 purchase totals = $892.78       $958.4297   $958.43   $958.45   $958.50