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 $188.45   6.810%   $201.2834   $201.28   $201.30   $201.30  
  Purchase #2 $239.49   11.176%   $266.2554   $266.26   $266.25   $266.30  
  Purchase #3 $30.76   10.317%   $33.9335   $33.93   $33.95   $33.90  
  Purchase #4 $118.60   10.449%   $130.9925   $130.99   $131.00   $131.00  
  Purchase #5 $175.27   7.279%   $188.0279   $188.03   $188.05   $188.00  
  Purchase #6 $225.88   9.835%   $248.0953   $248.10   $248.10   $248.10  
  Purchase #7 $117.91   12.851%   $133.0626   $133.06   $133.05   $133.10  
  7 purchase totals = $1,096.36       $1,201.6506   $1,201.65   $1,201.70   $1,201.70