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 $242.91   10.851%   $269.2682   $269.27   $269.25   $269.30  
  Purchase #2 $190.42   6.572%   $202.9344   $202.93   $202.95   $202.90  
  Purchase #3 $29.60   8.821%   $32.211   $32.21   $32.20   $32.20  
  Purchase #4 $109.54   12.352%   $123.0704   $123.07   $123.05   $123.10  
  Purchase #5 $205.46   5.241%   $216.2282   $216.23   $216.25   $216.20  
  Purchase #6 $76.36   3.741%   $79.2166   $79.22   $79.20   $79.20  
  Purchase #7 $105.37   4.146%   $109.7386   $109.74   $109.75   $109.70  
  7 purchase totals = $959.66       $1,032.6674   $1,032.67   $1,032.65   $1,032.60