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 $62.72   11.859%   $70.158   $70.16   $70.15   $70.20  
  Purchase #2 $10.38   11.420%   $11.5654   $11.57   $11.55   $11.60  
  Purchase #3 $152.66   9.727%   $167.5092   $167.51   $167.50   $167.50  
  Purchase #4 $191.97   12.304%   $215.59   $215.59   $215.60   $215.60  
  Purchase #5 $134.62   8.213%   $145.6763   $145.68   $145.70   $145.70  
  Purchase #6 $139.37   10.635%   $154.192   $154.19   $154.20   $154.20  
  Purchase #7 $60.48   11.706%   $67.5598   $67.56   $67.55   $67.60  
  7 purchase totals = $752.20       $832.2507   $832.26   $832.25   $832.40