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 $238.33   3.565%   $246.8265   $246.83   $246.85   $246.80  
  Purchase #2 $68.25   9.366%   $74.6423   $74.64   $74.65   $74.60  
  Purchase #3 $166.45   8.158%   $180.029   $180.03   $180.05   $180.00  
  Purchase #4 $248.57   9.551%   $272.3109   $272.31   $272.30   $272.30  
  Purchase #5 $229.62   11.661%   $256.396   $256.40   $256.40   $256.40  
  Purchase #6 $23.25   12.513%   $26.1593   $26.16   $26.15   $26.20  
  Purchase #7 $173.98   6.227%   $184.8137   $184.81   $184.80   $184.80  
  7 purchase totals = $1,148.45       $1,241.1777   $1,241.18   $1,241.20   $1,241.10