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 $156.45   4.615%   $163.6702   $163.67   $163.65   $163.70  
  Purchase #2 $220.94   8.374%   $239.4415   $239.44   $239.45   $239.40  
  Purchase #3 $48.91   6.772%   $52.2222   $52.22   $52.20   $52.20  
  Purchase #4 $195.31   12.777%   $220.2648   $220.26   $220.25   $220.30  
  Purchase #5 $173.47   6.863%   $185.3752   $185.38   $185.40   $185.40  
  Purchase #6 $123.32   4.199%   $128.4982   $128.50   $128.50   $128.50  
  Purchase #7 $64.29   13.519%   $72.9814   $72.98   $73.00   $73.00  
  7 purchase totals = $982.69       $1,062.4535   $1,062.45   $1,062.45   $1,062.50