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 $134.79   7.755%   $145.243   $145.24   $145.25   $145.20  
  Purchase #2 $138.80   7.240%   $148.8491   $148.85   $148.85   $148.80  
  Purchase #3 $79.41   6.680%   $84.7146   $84.71   $84.70   $84.70  
  Purchase #4 $215.88   4.735%   $226.1019   $226.10   $226.10   $226.10  
  Purchase #5 $23.89   12.110%   $26.7831   $26.78   $26.80   $26.80  
  Purchase #6 $139.46   4.153%   $145.2518   $145.25   $145.25   $145.30  
  Purchase #7 $239.63   4.319%   $249.9796   $249.98   $250.00   $250.00  
  7 purchase totals = $971.86       $1,026.9231   $1,026.91   $1,026.95   $1,026.90