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 $236.54   4.254%   $246.6024   $246.60   $246.60   $246.60  
  Purchase #2 $130.65   11.509%   $145.6865   $145.69   $145.70   $145.70  
  Purchase #3 $157.39   5.228%   $165.6183   $165.62   $165.60   $165.60  
  Purchase #4 $66.86   5.149%   $70.3026   $70.30   $70.30   $70.30  
  Purchase #5 $7.65   9.466%   $8.3741   $8.37   $8.35   $8.40  
  Purchase #6 $152.87   5.179%   $160.7871   $160.79   $160.80   $160.80  
  Purchase #7 $204.99   11.491%   $228.5454   $228.55   $228.55   $228.50  
  7 purchase totals = $956.95       $1,025.9164   $1,025.92   $1,025.90   $1,025.90