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 $68.33   8.738%   $74.3007   $74.30   $74.30   $74.30  
  Purchase #2 $141.75   11.626%   $158.2299   $158.23   $158.25   $158.20  
  Purchase #3 $27.94   5.124%   $29.3716   $29.37   $29.35   $29.40  
  Purchase #4 $44.33   3.668%   $45.956   $45.96   $45.95   $46.00  
  Purchase #5 $198.93   6.737%   $212.3319   $212.33   $212.35   $212.30  
  Purchase #6 $168.72   4.468%   $176.2584   $176.26   $176.25   $176.30  
  Purchase #7 $126.64   7.362%   $135.9632   $135.96   $135.95   $136.00  
  7 purchase totals = $776.64       $832.4117   $832.41   $832.40   $832.50