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 $63.33   9.359%   $69.2571   $69.26   $69.25   $69.30  
  Purchase #2 $176.61   6.401%   $187.9148   $187.91   $187.90   $187.90  
  Purchase #3 $210.51   5.445%   $221.9723   $221.97   $221.95   $222.00  
  Purchase #4 $211.63   8.820%   $230.2958   $230.30   $230.30   $230.30  
  Purchase #5 $235.68   5.154%   $247.8269   $247.83   $247.85   $247.80  
  Purchase #6 $72.99   10.340%   $80.5372   $80.54   $80.55   $80.50  
  Purchase #7 $158.97   5.802%   $168.1934   $168.19   $168.20   $168.20  
  7 purchase totals = $1,129.72       $1,205.9975   $1,206.00   $1,206.00   $1,206.00