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 $62.47   3.546%   $64.6852   $64.69   $64.70   $64.70  
  Purchase #2 $137.86   7.643%   $148.3966   $148.40   $148.40   $148.40  
  Purchase #3 $224.46   4.773%   $235.1735   $235.17   $235.15   $235.20  
  Purchase #4 $157.40   5.298%   $165.7391   $165.74   $165.75   $165.70  
  Purchase #5 $201.35   8.409%   $218.2815   $218.28   $218.30   $218.30  
  Purchase #6 $117.74   6.391%   $125.2648   $125.26   $125.25   $125.30  
  Purchase #7 $38.35   13.834%   $43.6553   $43.66   $43.65   $43.70  
  7 purchase totals = $939.63       $1,001.1960   $1,001.20   $1,001.20   $1,001.30