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 $62.36   8.402%   $67.5995   $67.60   $67.60   $67.60  
  Purchase #2 $185.71   12.402%   $208.7418   $208.74   $208.75   $208.70  
  Purchase #3 $213.26   5.301%   $224.5649   $224.56   $224.55   $224.60  
  Purchase #4 $141.52   9.627%   $155.1441   $155.14   $155.15   $155.10  
  Purchase #5 $191.27   9.850%   $210.1101   $210.11   $210.10   $210.10  
  Purchase #6 $214.40   11.787%   $239.6713   $239.67   $239.65   $239.70  
  Purchase #7 $175.84   13.102%   $198.8786   $198.88   $198.90   $198.90  
  7 purchase totals = $1,184.36       $1,304.7103   $1,304.70   $1,304.70   $1,304.70