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 $40.97   12.361%   $46.0343   $46.03   $46.05   $46.00  
  Purchase #2 $114.32   11.386%   $127.3365   $127.34   $127.35   $127.30  
  Purchase #3 $63.77   12.512%   $71.7489   $71.75   $71.75   $71.70  
  Purchase #4 $112.82   10.266%   $124.4021   $124.40   $124.40   $124.40  
  Purchase #5 $201.48   5.621%   $212.8052   $212.81   $212.80   $212.80  
  Purchase #6 $14.51   12.146%   $16.2724   $16.27   $16.25   $16.30  
  Purchase #7 $102.88   10.529%   $113.7122   $113.71   $113.70   $113.70  
  7 purchase totals = $650.75       $712.3116   $712.31   $712.30   $712.20