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 $115.85   7.229%   $124.2248   $124.22   $124.20   $124.20  
  Purchase #2 $161.38   3.476%   $166.9896   $166.99   $167.00   $167.00  
  Purchase #3 $147.87   5.476%   $155.9674   $155.97   $155.95   $156.00  
  Purchase #4 $159.87   10.369%   $176.4469   $176.45   $176.45   $176.40  
  Purchase #5 $99.95   8.493%   $108.4388   $108.44   $108.45   $108.40  
  Purchase #6 $61.65   8.607%   $66.9562   $66.96   $66.95   $67.00  
  Purchase #7 $229.72   7.217%   $246.2989   $246.30   $246.30   $246.30  
  7 purchase totals = $976.29       $1,045.3226   $1,045.33   $1,045.30   $1,045.30