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 $87.55   12.771%   $98.731   $98.73   $98.75   $98.70  
  Purchase #2 $236.74   7.413%   $254.2895   $254.29   $254.30   $254.30  
  Purchase #3 $237.93   8.719%   $258.6751   $258.68   $258.70   $258.70  
  Purchase #4 $29.94   7.783%   $32.2702   $32.27   $32.25   $32.30  
  Purchase #5 $117.26   12.439%   $131.846   $131.85   $131.85   $131.80  
  Purchase #6 $117.91   8.255%   $127.6435   $127.64   $127.65   $127.60  
  Purchase #7 $41.97   5.349%   $44.215   $44.22   $44.20   $44.20  
  7 purchase totals = $869.30       $947.6703   $947.68   $947.70   $947.60