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 $48.94   6.230%   $51.989   $51.99   $52.00   $52.00  
  Purchase #2 $114.37   12.337%   $128.4798   $128.48   $128.50   $128.50  
  Purchase #3 $234.83   8.563%   $254.9385   $254.94   $254.95   $254.90  
  Purchase #4 $233.78   8.662%   $254.03   $254.03   $254.05   $254.00  
  Purchase #5 $45.89   9.571%   $50.2821   $50.28   $50.30   $50.30  
  Purchase #6 $167.77   3.111%   $172.9893   $172.99   $173.00   $173.00  
  Purchase #7 $111.96   9.752%   $122.8783   $122.88   $122.90   $122.90  
  7 purchase totals = $957.54       $1,035.5870   $1,035.59   $1,035.70   $1,035.60