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 $173.33   8.183%   $187.5136   $187.51   $187.50   $187.50  
  Purchase #2 $61.95   6.461%   $65.9526   $65.95   $65.95   $66.00  
  Purchase #3 $130.61   4.443%   $136.413   $136.41   $136.40   $136.40  
  Purchase #4 $128.30   3.510%   $132.8033   $132.80   $132.80   $132.80  
  Purchase #5 $122.68   4.154%   $127.7761   $127.78   $127.80   $127.80  
  Purchase #6 $89.36   8.229%   $96.7134   $96.71   $96.70   $96.70  
  Purchase #7 $9.96   6.602%   $10.6176   $10.62   $10.60   $10.60  
  7 purchase totals = $716.19       $757.7896   $757.78   $757.75   $757.80