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 $26.61   11.366%   $29.6345   $29.63   $29.65   $29.60  
  Purchase #2 $124.97   7.751%   $134.6564   $134.66   $134.65   $134.70  
  Purchase #3 $239.91   3.517%   $248.3476   $248.35   $248.35   $248.30  
  Purchase #4 $220.65   11.367%   $245.7313   $245.73   $245.75   $245.70  
  Purchase #5 $95.72   5.124%   $100.6247   $100.62   $100.60   $100.60  
  Purchase #6 $157.88   13.819%   $179.6974   $179.70   $179.70   $179.70  
  Purchase #7 $129.49   11.708%   $144.6507   $144.65   $144.65   $144.70  
  7 purchase totals = $995.23       $1,083.3426   $1,083.34   $1,083.35   $1,083.30