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 $194.75   13.690%   $221.4113   $221.41   $221.40   $221.40  
  Purchase #2 $23.53   7.588%   $25.3155   $25.32   $25.30   $25.30  
  Purchase #3 $67.62   12.851%   $76.3098   $76.31   $76.30   $76.30  
  Purchase #4 $115.57   9.672%   $126.7479   $126.75   $126.75   $126.70  
  Purchase #5 $14.63   6.808%   $15.626   $15.63   $15.65   $15.60  
  Purchase #6 $93.74   13.547%   $106.439   $106.44   $106.45   $106.40  
  Purchase #7 $179.52   7.816%   $193.5513   $193.55   $193.55   $193.60  
  7 purchase totals = $689.36       $765.4008   $765.41   $765.40   $765.30