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 $233.57   11.296%   $259.9541   $259.95   $259.95   $260.00  
  Purchase #2 $80.86   6.815%   $86.3706   $86.37   $86.35   $86.40  
  Purchase #3 $84.84   13.215%   $96.0516   $96.05   $96.05   $96.10  
  Purchase #4 $127.60   8.416%   $138.3388   $138.34   $138.35   $138.30  
  Purchase #5 $219.59   10.427%   $242.4866   $242.49   $242.50   $242.50  
  Purchase #6 $221.42   8.362%   $239.9351   $239.94   $239.95   $239.90  
  Purchase #7 $11.56   12.668%   $13.0244   $13.02   $13.00   $13.00  
  7 purchase totals = $979.44       $1,076.1612   $1,076.16   $1,076.15   $1,076.20