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 $193.62   11.393%   $215.6791   $215.68   $215.70   $215.70  
  Purchase #2 $202.77   13.147%   $229.4282   $229.43   $229.45   $229.40  
  Purchase #3 $21.90   5.716%   $23.1518   $23.15   $23.15   $23.20  
  Purchase #4 $248.28   9.477%   $271.8095   $271.81   $271.80   $271.80  
  Purchase #5 $201.36   10.219%   $221.937   $221.94   $221.95   $221.90  
  Purchase #6 $7.55   4.666%   $7.9023   $7.90   $7.90   $7.90  
  Purchase #7 $54.84   10.702%   $60.709   $60.71   $60.70   $60.70  
  7 purchase totals = $930.32       $1,030.6169   $1,030.62   $1,030.65   $1,030.60