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 $213.93   6.660%   $228.1777   $228.18   $228.20   $228.20  
  Purchase #2 $218.81   5.416%   $230.6607   $230.66   $230.65   $230.70  
  Purchase #3 $147.25   3.848%   $152.9162   $152.92   $152.90   $152.90  
  Purchase #4 $153.59   9.271%   $167.8293   $167.83   $167.85   $167.80  
  Purchase #5 $10.68   6.607%   $11.3856   $11.39   $11.40   $11.40  
  Purchase #6 $21.99   3.131%   $22.6785   $22.68   $22.70   $22.70  
  Purchase #7 $228.77   9.420%   $250.3201   $250.32   $250.30   $250.30  
  7 purchase totals = $995.02       $1,063.9681   $1,063.98   $1,064.00   $1,064.00