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 $231.30   6.762%   $246.9405   $246.94   $246.95   $246.90  
  Purchase #2 $65.76   12.630%   $74.0655   $74.07   $74.05   $74.10  
  Purchase #3 $140.84   3.635%   $145.9595   $145.96   $145.95   $146.00  
  Purchase #4 $154.70   7.554%   $166.386   $166.39   $166.40   $166.40  
  Purchase #5 $213.35   8.355%   $231.1754   $231.18   $231.20   $231.20  
  Purchase #6 $26.64   9.279%   $29.1119   $29.11   $29.10   $29.10  
  Purchase #7 $61.68   4.233%   $64.2909   $64.29   $64.30   $64.30  
  7 purchase totals = $894.27       $957.9297   $957.94   $957.95   $958.00