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 $60.83   9.628%   $66.6867   $66.69   $66.70   $66.70  
  Purchase #2 $206.69   9.258%   $225.8254   $225.83   $225.85   $225.80  
  Purchase #3 $89.91   8.500%   $97.5524   $97.55   $97.55   $97.60  
  Purchase #4 $235.44   5.333%   $247.996   $248.00   $248.00   $248.00  
  Purchase #5 $119.78   8.813%   $130.3362   $130.34   $130.35   $130.30  
  Purchase #6 $7.61   5.553%   $8.0326   $8.03   $8.05   $8.00  
  Purchase #7 $138.37   6.131%   $146.8535   $146.85   $146.85   $146.90  
  7 purchase totals = $858.63       $923.2828   $923.29   $923.35   $923.30