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 $154.52   11.716%   $172.6236   $172.62   $172.60   $172.60  
  Purchase #2 $22.63   11.356%   $25.1999   $25.20   $25.20   $25.20  
  Purchase #3 $151.86   11.855%   $169.863   $169.86   $169.85   $169.90  
  Purchase #4 $126.79   7.216%   $135.9392   $135.94   $135.95   $135.90  
  Purchase #5 $246.84   6.253%   $262.2749   $262.27   $262.25   $262.30  
  Purchase #6 $57.51   8.802%   $62.572   $62.57   $62.55   $62.60  
  Purchase #7 $220.44   8.858%   $239.9666   $239.97   $239.95   $240.00  
  7 purchase totals = $980.59       $1,068.4392   $1,068.43   $1,068.35   $1,068.50