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 $240.61   4.816%   $252.1978   $252.20   $252.20   $252.20  
  Purchase #2 $211.93   12.225%   $237.8384   $237.84   $237.85   $237.80  
  Purchase #3 $150.92   11.620%   $168.4569   $168.46   $168.45   $168.50  
  Purchase #4 $132.36   11.116%   $147.0731   $147.07   $147.05   $147.10  
  Purchase #5 $58.70   6.864%   $62.7292   $62.73   $62.75   $62.70  
  Purchase #6 $243.61   7.464%   $261.7931   $261.79   $261.80   $261.80  
  Purchase #7 $180.35   3.816%   $187.2322   $187.23   $187.25   $187.20  
  7 purchase totals = $1,218.48       $1,317.3207   $1,317.32   $1,317.35   $1,317.30