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 $40.66   9.595%   $44.5613   $44.56   $44.55   $44.60  
  Purchase #2 $147.89   13.157%   $167.3479   $167.35   $167.35   $167.30  
  Purchase #3 $111.53   10.782%   $123.5552   $123.56   $123.55   $123.60  
  Purchase #4 $230.66   6.859%   $246.481   $246.48   $246.50   $246.50  
  Purchase #5 $218.86   8.367%   $237.172   $237.17   $237.15   $237.20  
  Purchase #6 $147.78   10.360%   $163.09   $163.09   $163.10   $163.10  
  Purchase #7 $202.60   6.423%   $215.613   $215.61   $215.60   $215.60  
  7 purchase totals = $1,099.98       $1,197.8204   $1,197.82   $1,197.80   $1,197.90