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 $248.57   6.609%   $264.998   $265.00   $265.00   $265.00  
  Purchase #2 $8.53   10.703%   $9.443   $9.44   $9.45   $9.40  
  Purchase #3 $182.52   6.366%   $194.1392   $194.14   $194.15   $194.10  
  Purchase #4 $197.60   5.437%   $208.3435   $208.34   $208.35   $208.30  
  Purchase #5 $134.64   9.413%   $147.3137   $147.31   $147.30   $147.30  
  Purchase #6 $179.74   3.870%   $186.6959   $186.70   $186.70   $186.70  
  Purchase #7 $51.52   6.629%   $54.9353   $54.94   $54.95   $54.90  
  7 purchase totals = $1,003.12       $1,065.8686   $1,065.87   $1,065.90   $1,065.70