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 $66.55   10.602%   $73.6056   $73.61   $73.60   $73.60  
  Purchase #2 $196.88   10.543%   $217.6371   $217.64   $217.65   $217.60  
  Purchase #3 $155.62   3.261%   $160.6948   $160.69   $160.70   $160.70  
  Purchase #4 $223.86   13.464%   $254.0005   $254.00   $254.00   $254.00  
  Purchase #5 $182.27   8.459%   $197.6882   $197.69   $197.70   $197.70  
  Purchase #6 $98.62   9.341%   $107.8321   $107.83   $107.85   $107.80  
  Purchase #7 $212.99   10.438%   $235.2219   $235.22   $235.20   $235.20  
  7 purchase totals = $1,136.79       $1,246.6802   $1,246.68   $1,246.70   $1,246.60