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 $58.61   13.669%   $66.6214   $66.62   $66.60   $66.60  
  Purchase #2 $161.36   3.431%   $166.8963   $166.90   $166.90   $166.90  
  Purchase #3 $33.96   10.582%   $37.5536   $37.55   $37.55   $37.60  
  Purchase #4 $245.56   11.485%   $273.7626   $273.76   $273.75   $273.80  
  Purchase #5 $14.85   11.658%   $16.5812   $16.58   $16.60   $16.60  
  Purchase #6 $231.36   9.222%   $252.696   $252.70   $252.70   $252.70  
  Purchase #7 $174.99   12.853%   $197.4815   $197.48   $197.50   $197.50  
  7 purchase totals = $920.69       $1,011.5926   $1,011.59   $1,011.60   $1,011.70