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 $68.76   8.226%   $74.4162   $74.42   $74.40   $74.40  
  Purchase #2 $38.98   6.459%   $41.4977   $41.50   $41.50   $41.50  
  Purchase #3 $236.78   7.141%   $253.6885   $253.69   $253.70   $253.70  
  Purchase #4 $132.96   9.292%   $145.3146   $145.31   $145.30   $145.30  
  Purchase #5 $246.86   6.565%   $263.0664   $263.07   $263.05   $263.10  
  Purchase #6 $171.56   5.146%   $180.3885   $180.39   $180.40   $180.40  
  Purchase #7 $8.75   9.626%   $9.5923   $9.59   $9.60   $9.60  
  7 purchase totals = $904.65       $967.9642   $967.97   $967.95   $968.00