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 $226.70   8.651%   $246.3118   $246.31   $246.30   $246.30  
  Purchase #2 $233.94   11.710%   $261.3344   $261.33   $261.35   $261.30  
  Purchase #3 $210.54   7.615%   $226.5726   $226.57   $226.55   $226.60  
  Purchase #4 $30.48   8.836%   $33.1732   $33.17   $33.15   $33.20  
  Purchase #5 $222.76   9.836%   $244.6707   $244.67   $244.65   $244.70  
  Purchase #6 $143.67   4.600%   $150.2788   $150.28   $150.30   $150.30  
  Purchase #7 $73.96   3.133%   $76.2772   $76.28   $76.30   $76.30  
  7 purchase totals = $1,142.05       $1,238.6187   $1,238.61   $1,238.60   $1,238.70