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 $116.79   5.282%   $122.9588   $122.96   $122.95   $123.00  
  Purchase #2 $199.85   3.598%   $207.0406   $207.04   $207.05   $207.00  
  Purchase #3 $31.85   12.327%   $35.7761   $35.78   $35.80   $35.80  
  Purchase #4 $124.66   5.766%   $131.8479   $131.85   $131.85   $131.80  
  Purchase #5 $79.87   4.526%   $83.4849   $83.48   $83.50   $83.50  
  Purchase #6 $109.70   6.848%   $117.2123   $117.21   $117.20   $117.20  
  Purchase #7 $53.33   13.738%   $60.6565   $60.66   $60.65   $60.70  
  7 purchase totals = $716.05       $758.9771   $758.98   $759.00   $759.00