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 $50.77   11.588%   $56.6532   $56.65   $56.65   $56.70  
  Purchase #2 $214.95   12.184%   $241.1395   $241.14   $241.15   $241.10  
  Purchase #3 $242.96   6.393%   $258.4924   $258.49   $258.50   $258.50  
  Purchase #4 $31.66   7.836%   $34.1409   $34.14   $34.15   $34.10  
  Purchase #5 $239.66   8.237%   $259.4008   $259.40   $259.40   $259.40  
  Purchase #6 $200.48   4.413%   $209.3272   $209.33   $209.35   $209.30  
  Purchase #7 $113.98   7.272%   $122.2686   $122.27   $122.25   $122.30  
  7 purchase totals = $1,094.46       $1,181.4226   $1,181.42   $1,181.45   $1,181.40