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 $178.47   10.808%   $197.759   $197.76   $197.75   $197.80  
  Purchase #2 $244.62   3.115%   $252.2399   $252.24   $252.25   $252.20  
  Purchase #3 $123.31   13.483%   $139.9359   $139.94   $139.95   $139.90  
  Purchase #4 $17.55   7.564%   $18.8775   $18.88   $18.90   $18.90  
  Purchase #5 $133.65   5.656%   $141.2092   $141.21   $141.20   $141.20  
  Purchase #6 $205.30   6.138%   $217.9013   $217.90   $217.90   $217.90  
  Purchase #7 $86.51   10.271%   $95.3954   $95.40   $95.40   $95.40  
  7 purchase totals = $989.41       $1,063.3182   $1,063.33   $1,063.35   $1,063.30