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 $218.87   6.274%   $232.6019   $232.60   $232.60   $232.60  
  Purchase #2 $119.99   9.548%   $131.4466   $131.45   $131.45   $131.40  
  Purchase #3 $120.58   12.494%   $135.6453   $135.65   $135.65   $135.60  
  Purchase #4 $189.61   13.675%   $215.5392   $215.54   $215.55   $215.50  
  Purchase #5 $217.71   6.629%   $232.142   $232.14   $232.15   $232.10  
  Purchase #6 $62.55   11.530%   $69.762   $69.76   $69.75   $69.80  
  Purchase #7 $236.55   7.153%   $253.4704   $253.47   $253.45   $253.50  
  7 purchase totals = $1,165.86       $1,270.6074   $1,270.61   $1,270.60   $1,270.50