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 $134.99   4.315%   $140.8148   $140.81   $140.80   $140.80  
  Purchase #2 $116.37   11.701%   $129.9865   $129.99   $130.00   $130.00  
  Purchase #3 $136.46   13.555%   $154.9572   $154.96   $154.95   $155.00  
  Purchase #4 $19.97   13.161%   $22.5983   $22.60   $22.60   $22.60  
  Purchase #5 $250.91   10.665%   $277.6696   $277.67   $277.65   $277.70  
  Purchase #6 $159.98   12.668%   $180.2463   $180.25   $180.25   $180.20  
  Purchase #7 $247.77   3.386%   $256.1595   $256.16   $256.15   $256.20  
  7 purchase totals = $1,066.45       $1,162.4322   $1,162.44   $1,162.40   $1,162.50