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 $59.29   4.158%   $61.7553   $61.76   $61.75   $61.80  
  Purchase #2 $249.44   6.649%   $266.0253   $266.03   $266.05   $266.00  
  Purchase #3 $40.34   4.855%   $42.2985   $42.30   $42.30   $42.30  
  Purchase #4 $194.84   8.435%   $211.2748   $211.27   $211.25   $211.30  
  Purchase #5 $195.28   7.506%   $209.9377   $209.94   $209.95   $209.90  
  Purchase #6 $70.55   13.376%   $79.9868   $79.99   $80.00   $80.00  
  Purchase #7 $48.67   6.843%   $52.0005   $52.00   $52.00   $52.00  
  7 purchase totals = $858.41       $923.2789   $923.29   $923.30   $923.30