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 $53.98   13.311%   $61.1653   $61.17   $61.15   $61.20  
  Purchase #2 $173.38   7.822%   $186.9418   $186.94   $186.95   $186.90  
  Purchase #3 $178.32   8.366%   $193.2383   $193.24   $193.25   $193.20  
  Purchase #4 $78.54   7.388%   $84.3425   $84.34   $84.35   $84.30  
  Purchase #5 $226.88   7.506%   $243.9096   $243.91   $243.90   $243.90  
  Purchase #6 $121.90   4.749%   $127.689   $127.69   $127.70   $127.70  
  Purchase #7 $127.40   3.776%   $132.2106   $132.21   $132.20   $132.20  
  7 purchase totals = $960.40       $1,029.4971   $1,029.50   $1,029.50   $1,029.40