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 $107.43   6.805%   $114.7406   $114.74   $114.75   $114.70  
  Purchase #2 $60.78   13.450%   $68.9549   $68.95   $68.95   $69.00  
  Purchase #3 $65.60   12.620%   $73.8787   $73.88   $73.90   $73.90  
  Purchase #4 $64.93   10.793%   $71.9379   $71.94   $71.95   $71.90  
  Purchase #5 $85.62   12.505%   $96.3268   $96.33   $96.35   $96.30  
  Purchase #6 $187.69   6.256%   $199.4319   $199.43   $199.45   $199.40  
  Purchase #7 $96.61   10.270%   $106.5318   $106.53   $106.55   $106.50  
  7 purchase totals = $668.66       $731.8026   $731.80   $731.90   $731.70