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 $244.97   8.189%   $265.0306   $265.03   $265.05   $265.00  
  Purchase #2 $91.37   5.275%   $96.1898   $96.19   $96.20   $96.20  
  Purchase #3 $155.28   6.863%   $165.9369   $165.94   $165.95   $165.90  
  Purchase #4 $66.67   6.668%   $71.1156   $71.12   $71.10   $71.10  
  Purchase #5 $180.90   8.340%   $195.9871   $195.99   $196.00   $196.00  
  Purchase #6 $84.33   11.653%   $94.157   $94.16   $94.15   $94.20  
  Purchase #7 $38.27   13.751%   $43.5325   $43.53   $43.55   $43.50  
  7 purchase totals = $861.79       $931.9495   $931.96   $932.00   $931.90