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 $86.76   6.378%   $92.2936   $92.29   $92.30   $92.30  
  Purchase #2 $153.49   6.391%   $163.2995   $163.30   $163.30   $163.30  
  Purchase #3 $230.64   11.721%   $257.6733   $257.67   $257.65   $257.70  
  Purchase #4 $123.63   8.864%   $134.5886   $134.59   $134.60   $134.60  
  Purchase #5 $171.85   13.168%   $194.4792   $194.48   $194.50   $194.50  
  Purchase #6 $170.36   13.708%   $193.7129   $193.71   $193.70   $193.70  
  Purchase #7 $196.69   6.802%   $210.0689   $210.07   $210.05   $210.10  
  7 purchase totals = $1,133.42       $1,246.1160   $1,246.11   $1,246.10   $1,246.20