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 $88.32   11.871%   $98.8045   $98.80   $98.80   $98.80  
  Purchase #2 $206.90   13.704%   $235.2536   $235.25   $235.25   $235.30  
  Purchase #3 $177.35   13.219%   $200.7939   $200.79   $200.80   $200.80  
  Purchase #4 $49.99   3.544%   $51.7616   $51.76   $51.75   $51.80  
  Purchase #5 $145.85   3.436%   $150.8614   $150.86   $150.85   $150.90  
  Purchase #6 $214.62   10.832%   $237.8676   $237.87   $237.85   $237.90  
  Purchase #7 $79.73   6.459%   $84.8798   $84.88   $84.90   $84.90  
  7 purchase totals = $962.76       $1,060.2224   $1,060.21   $1,060.20   $1,060.40