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 $244.88   9.615%   $268.4252   $268.43   $268.45   $268.40  
  Purchase #2 $91.59   12.153%   $102.7209   $102.72   $102.70   $102.70  
  Purchase #3 $85.32   5.347%   $89.8821   $89.88   $89.90   $89.90  
  Purchase #4 $58.42   4.300%   $60.9321   $60.93   $60.95   $60.90  
  Purchase #5 $176.75   9.732%   $193.9513   $193.95   $193.95   $194.00  
  Purchase #6 $186.65   11.486%   $208.0886   $208.09   $208.10   $208.10  
  Purchase #7 $35.53   4.210%   $37.0258   $37.03   $37.05   $37.00  
  7 purchase totals = $879.14       $961.0260   $961.03   $961.10   $961.00