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 $165.65   5.722%   $175.1285   $175.13   $175.15   $175.10  
  Purchase #2 $25.99   13.491%   $29.4963   $29.50   $29.50   $29.50  
  Purchase #3 $167.62   5.332%   $176.5575   $176.56   $176.55   $176.60  
  Purchase #4 $27.45   5.484%   $28.9554   $28.96   $28.95   $29.00  
  Purchase #5 $218.67   3.182%   $225.6281   $225.63   $225.65   $225.60  
  Purchase #6 $243.46   4.847%   $255.2605   $255.26   $255.25   $255.30  
  Purchase #7 $18.60   10.405%   $20.5353   $20.54   $20.55   $20.50  
  7 purchase totals = $867.44       $911.5616   $911.58   $911.60   $911.60