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 $168.81   8.510%   $183.1757   $183.18   $183.20   $183.20  
  Purchase #2 $235.37   4.767%   $246.5901   $246.59   $246.60   $246.60  
  Purchase #3 $205.52   5.226%   $216.2605   $216.26   $216.25   $216.30  
  Purchase #4 $132.60   6.202%   $140.8239   $140.82   $140.80   $140.80  
  Purchase #5 $20.71   5.718%   $21.8942   $21.89   $21.90   $21.90  
  Purchase #6 $132.55   4.464%   $138.467   $138.47   $138.45   $138.50  
  Purchase #7 $60.62   13.585%   $68.8552   $68.86   $68.85   $68.90  
  7 purchase totals = $956.18       $1,016.0666   $1,016.07   $1,016.05   $1,016.20