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 $161.34   8.649%   $175.2943   $175.29   $175.30   $175.30  
  Purchase #2 $6.97   9.713%   $7.647   $7.65   $7.65   $7.60  
  Purchase #3 $136.32   7.139%   $146.0519   $146.05   $146.05   $146.10  
  Purchase #4 $240.32   9.235%   $262.5136   $262.51   $262.50   $262.50  
  Purchase #5 $65.38   9.467%   $71.5695   $71.57   $71.55   $71.60  
  Purchase #6 $163.58   3.494%   $169.2955   $169.30   $169.30   $169.30  
  Purchase #7 $116.29   9.827%   $127.7178   $127.72   $127.70   $127.70  
  7 purchase totals = $890.20       $960.0896   $960.09   $960.05   $960.10