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 $96.96   5.872%   $102.6535   $102.65   $102.65   $102.70  
  Purchase #2 $18.97   5.248%   $19.9655   $19.97   $19.95   $20.00  
  Purchase #3 $68.96   6.841%   $73.6776   $73.68   $73.70   $73.70  
  Purchase #4 $60.62   8.695%   $65.8909   $65.89   $65.90   $65.90  
  Purchase #5 $144.54   7.247%   $155.0148   $155.01   $155.00   $155.00  
  Purchase #6 $237.51   4.623%   $248.4901   $248.49   $248.50   $248.50  
  Purchase #7 $95.46   4.203%   $99.4722   $99.47   $99.45   $99.50  
  7 purchase totals = $723.02       $765.1646   $765.16   $765.15   $765.30