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 $147.82   8.474%   $160.3463   $160.35   $160.35   $160.30  
  Purchase #2 $245.37   6.310%   $260.8528   $260.85   $260.85   $260.90  
  Purchase #3 $30.99   7.242%   $33.2343   $33.23   $33.25   $33.20  
  Purchase #4 $48.83   13.509%   $55.4264   $55.43   $55.45   $55.40  
  Purchase #5 $192.37   7.449%   $206.6996   $206.70   $206.70   $206.70  
  Purchase #6 $133.74   3.676%   $138.6563   $138.66   $138.65   $138.70  
  Purchase #7 $102.27   9.353%   $111.8353   $111.84   $111.85   $111.80  
  7 purchase totals = $901.39       $967.0510   $967.06   $967.10   $967.00