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 $54.56   13.688%   $62.0282   $62.03   $62.05   $62.00  
  Purchase #2 $117.64   7.232%   $126.1477   $126.15   $126.15   $126.10  
  Purchase #3 $20.99   11.472%   $23.398   $23.40   $23.40   $23.40  
  Purchase #4 $26.67   3.204%   $27.5245   $27.52   $27.50   $27.50  
  Purchase #5 $110.38   9.532%   $120.9014   $120.90   $120.90   $120.90  
  Purchase #6 $131.59   10.433%   $145.3188   $145.32   $145.30   $145.30  
  Purchase #7 $182.74   4.835%   $191.5755   $191.58   $191.60   $191.60  
  7 purchase totals = $644.57       $696.8941   $696.90   $696.90   $696.80