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 $86.87   6.111%   $92.1786   $92.18   $92.20   $92.20  
  Purchase #2 $61.75   6.853%   $65.9817   $65.98   $66.00   $66.00  
  Purchase #3 $188.46   6.585%   $200.8701   $200.87   $200.85   $200.90  
  Purchase #4 $222.51   11.441%   $247.9674   $247.97   $247.95   $248.00  
  Purchase #5 $219.96   9.557%   $240.9816   $240.98   $241.00   $241.00  
  Purchase #6 $65.35   12.538%   $73.5436   $73.54   $73.55   $73.50  
  Purchase #7 $248.73   13.627%   $282.6244   $282.62   $282.60   $282.60  
  7 purchase totals = $1,093.63       $1,204.1474   $1,204.14   $1,204.15   $1,204.20