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 $69.89   5.602%   $73.8052   $73.81   $73.80   $73.80  
  Purchase #2 $101.91   13.474%   $115.6414   $115.64   $115.65   $115.60  
  Purchase #3 $128.68   5.159%   $135.3186   $135.32   $135.30   $135.30  
  Purchase #4 $237.82   10.412%   $262.5818   $262.58   $262.60   $262.60  
  Purchase #5 $18.77   12.285%   $21.0759   $21.08   $21.10   $21.10  
  Purchase #6 $186.33   12.435%   $209.5001   $209.50   $209.50   $209.50  
  Purchase #7 $195.35   5.488%   $206.0708   $206.07   $206.05   $206.10  
  7 purchase totals = $938.75       $1,023.9938   $1,024.00   $1,024.00   $1,024.00