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 $63.34   11.451%   $70.5931   $70.59   $70.60   $70.60  
  Purchase #2 $103.80   9.686%   $113.8541   $113.85   $113.85   $113.90  
  Purchase #3 $116.27   9.461%   $127.2703   $127.27   $127.25   $127.30  
  Purchase #4 $82.82   4.475%   $86.5262   $86.53   $86.55   $86.50  
  Purchase #5 $171.72   5.253%   $180.7405   $180.74   $180.75   $180.70  
  Purchase #6 $22.79   4.511%   $23.8181   $23.82   $23.80   $23.80  
  Purchase #7 $212.47   6.457%   $226.1892   $226.19   $226.20   $226.20  
  7 purchase totals = $773.21       $828.9915   $828.99   $829.00   $829.00