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 $76.60   13.552%   $86.9808   $86.98   $87.00   $87.00  
  Purchase #2 $108.96   5.391%   $114.834   $114.83   $114.85   $114.80  
  Purchase #3 $245.27   13.203%   $277.653   $277.65   $277.65   $277.70  
  Purchase #4 $95.36   8.357%   $103.3292   $103.33   $103.35   $103.30  
  Purchase #5 $211.90   9.563%   $232.164   $232.16   $232.15   $232.20  
  Purchase #6 $41.66   8.599%   $45.2423   $45.24   $45.25   $45.20  
  Purchase #7 $116.39   7.292%   $124.8772   $124.88   $124.90   $124.90  
  7 purchase totals = $896.14       $985.0805   $985.07   $985.15   $985.10