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 $110.96   5.482%   $117.0428   $117.04   $117.05   $117.00  
  Purchase #2 $21.55   9.246%   $23.5425   $23.54   $23.55   $23.50  
  Purchase #3 $35.47   3.627%   $36.7565   $36.76   $36.75   $36.80  
  Purchase #4 $97.55   11.612%   $108.8775   $108.88   $108.90   $108.90  
  Purchase #5 $209.55   10.514%   $231.5821   $231.58   $231.60   $231.60  
  Purchase #6 $48.32   11.716%   $53.9812   $53.98   $54.00   $54.00  
  Purchase #7 $171.40   12.732%   $193.2226   $193.22   $193.20   $193.20  
  7 purchase totals = $694.80       $765.0052   $765.00   $765.05   $765.00