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 $153.85   11.252%   $171.1612   $171.16   $171.15   $171.20  
  Purchase #2 $173.43   9.785%   $190.4001   $190.40   $190.40   $190.40  
  Purchase #3 $69.82   7.391%   $74.9804   $74.98   $75.00   $75.00  
  Purchase #4 $26.83   11.772%   $29.9884   $29.99   $30.00   $30.00  
  Purchase #5 $209.80   7.725%   $226.0071   $226.01   $226.00   $226.00  
  Purchase #6 $124.57   8.128%   $134.695   $134.70   $134.70   $134.70  
  Purchase #7 $183.25   12.761%   $206.6345   $206.63   $206.65   $206.60  
  7 purchase totals = $941.55       $1,033.8667   $1,033.87   $1,033.90   $1,033.90