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 $68.89   3.509%   $71.3074   $71.31   $71.30   $71.30  
  Purchase #2 $105.33   11.392%   $117.3292   $117.33   $117.35   $117.30  
  Purchase #3 $164.53   4.508%   $171.947   $171.95   $171.95   $171.90  
  Purchase #4 $212.68   10.803%   $235.6558   $235.66   $235.65   $235.70  
  Purchase #5 $131.60   12.356%   $147.8605   $147.86   $147.85   $147.90  
  Purchase #6 $6.44   4.503%   $6.73   $6.73   $6.75   $6.70  
  Purchase #7 $21.70   7.279%   $23.2795   $23.28   $23.30   $23.30  
  7 purchase totals = $711.17       $774.1094   $774.12   $774.15   $774.10