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 $226.81   9.616%   $248.62   $248.62   $248.60   $248.60  
  Purchase #2 $66.25   3.611%   $68.6423   $68.64   $68.65   $68.60  
  Purchase #3 $232.94   12.869%   $262.917   $262.92   $262.90   $262.90  
  Purchase #4 $192.47   12.205%   $215.961   $215.96   $215.95   $216.00  
  Purchase #5 $132.41   4.305%   $138.1103   $138.11   $138.10   $138.10  
  Purchase #6 $73.80   4.684%   $77.2568   $77.26   $77.25   $77.30  
  Purchase #7 $200.95   5.582%   $212.167   $212.17   $212.15   $212.20  
  7 purchase totals = $1,125.63       $1,223.6744   $1,223.68   $1,223.60   $1,223.70