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 $93.48   5.479%   $98.6018   $98.60   $98.60   $98.60  
  Purchase #2 $132.73   5.619%   $140.1881   $140.19   $140.20   $140.20  
  Purchase #3 $126.79   5.166%   $133.34   $133.34   $133.35   $133.30  
  Purchase #4 $84.36   13.498%   $95.7469   $95.75   $95.75   $95.70  
  Purchase #5 $211.47   4.629%   $221.2589   $221.26   $221.25   $221.30  
  Purchase #6 $206.66   13.833%   $235.2473   $235.25   $235.25   $235.20  
  Purchase #7 $117.37   8.671%   $127.5472   $127.55   $127.55   $127.50  
  7 purchase totals = $972.86       $1,051.9302   $1,051.94   $1,051.95   $1,051.80