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 $63.67   8.293%   $68.9502   $68.95   $68.95   $69.00  
  Purchase #2 $102.88   3.148%   $106.1187   $106.12   $106.10   $106.10  
  Purchase #3 $81.36   4.677%   $85.1652   $85.17   $85.15   $85.20  
  Purchase #4 $205.58   8.757%   $223.5826   $223.58   $223.60   $223.60  
  Purchase #5 $246.48   12.154%   $276.4372   $276.44   $276.45   $276.40  
  Purchase #6 $73.97   3.314%   $76.4214   $76.42   $76.40   $76.40  
  Purchase #7 $42.54   5.595%   $44.9201   $44.92   $44.90   $44.90  
  7 purchase totals = $816.48       $881.5954   $881.60   $881.55   $881.60