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 $169.57   4.832%   $177.7636   $177.76   $177.75   $177.80  
  Purchase #2 $61.96   11.265%   $68.9398   $68.94   $68.95   $68.90  
  Purchase #3 $192.38   11.163%   $213.8554   $213.86   $213.85   $213.90  
  Purchase #4 $196.86   12.454%   $221.3769   $221.38   $221.40   $221.40  
  Purchase #5 $9.94   6.791%   $10.615   $10.62   $10.60   $10.60  
  Purchase #6 $206.66   4.528%   $216.0176   $216.02   $216.00   $216.00  
  Purchase #7 $56.58   5.368%   $59.6172   $59.62   $59.60   $59.60  
  7 purchase totals = $893.95       $968.1855   $968.20   $968.15   $968.20