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 $59.99   5.397%   $63.2277   $63.23   $63.25   $63.20  
  Purchase #2 $216.53   11.716%   $241.8987   $241.90   $241.90   $241.90  
  Purchase #3 $115.95   13.410%   $131.4989   $131.50   $131.50   $131.50  
  Purchase #4 $162.42   4.726%   $170.096   $170.10   $170.10   $170.10  
  Purchase #5 $182.43   11.728%   $203.8254   $203.83   $203.85   $203.80  
  Purchase #6 $99.57   5.481%   $105.0274   $105.03   $105.05   $105.00  
  Purchase #7 $63.76   5.121%   $67.0251   $67.03   $67.05   $67.00  
  7 purchase totals = $900.65       $982.5992   $982.62   $982.70   $982.50