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 $144.60   12.501%   $162.6764   $162.68   $162.70   $162.70  
  Purchase #2 $213.69   7.851%   $230.4668   $230.47   $230.45   $230.50  
  Purchase #3 $116.56   11.274%   $129.701   $129.70   $129.70   $129.70  
  Purchase #4 $90.82   12.231%   $101.9282   $101.93   $101.95   $101.90  
  Purchase #5 $245.25   8.526%   $266.16   $266.16   $266.15   $266.20  
  Purchase #6 $188.29   6.775%   $201.0466   $201.05   $201.05   $201.00  
  Purchase #7 $91.61   12.692%   $103.2371   $103.24   $103.25   $103.20  
  7 purchase totals = $1,090.82       $1,195.2161   $1,195.23   $1,195.25   $1,195.20