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 $53.39   7.380%   $57.3302   $57.33   $57.35   $57.30  
  Purchase #2 $248.34   11.114%   $275.9405   $275.94   $275.95   $275.90  
  Purchase #3 $23.67   5.220%   $24.9056   $24.91   $24.90   $24.90  
  Purchase #4 $56.52   10.484%   $62.4456   $62.45   $62.45   $62.40  
  Purchase #5 $152.62   9.612%   $167.2898   $167.29   $167.30   $167.30  
  Purchase #6 $184.92   4.855%   $193.8979   $193.90   $193.90   $193.90  
  Purchase #7 $44.81   3.601%   $46.4236   $46.42   $46.40   $46.40  
  7 purchase totals = $764.27       $828.2332   $828.24   $828.25   $828.10