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 $222.44   6.802%   $237.5704   $237.57   $237.55   $237.60  
  Purchase #2 $119.93   13.106%   $135.648   $135.65   $135.65   $135.60  
  Purchase #3 $111.65   8.371%   $120.9962   $121.00   $121.00   $121.00  
  Purchase #4 $192.57   9.812%   $211.465   $211.47   $211.45   $211.50  
  Purchase #5 $190.54   6.468%   $202.8641   $202.86   $202.85   $202.90  
  Purchase #6 $114.84   9.458%   $125.7016   $125.70   $125.70   $125.70  
  Purchase #7 $122.68   11.652%   $136.9747   $136.97   $136.95   $137.00  
  7 purchase totals = $1,074.65       $1,171.2200   $1,171.22   $1,171.15   $1,171.30