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 $208.42   8.726%   $226.6067   $226.61   $226.60   $226.60  
  Purchase #2 $235.68   11.836%   $263.5751   $263.58   $263.60   $263.60  
  Purchase #3 $148.47   3.731%   $154.0094   $154.01   $154.00   $154.00  
  Purchase #4 $86.42   6.103%   $91.6942   $91.69   $91.70   $91.70  
  Purchase #5 $250.28   13.864%   $284.9788   $284.98   $285.00   $285.00  
  Purchase #6 $135.59   12.803%   $152.9496   $152.95   $152.95   $152.90  
  Purchase #7 $35.77   11.719%   $39.9619   $39.96   $39.95   $40.00  
  7 purchase totals = $1,100.63       $1,213.7757   $1,213.78   $1,213.80   $1,213.80