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 $155.88   4.691%   $163.1923   $163.19   $163.20   $163.20  
  Purchase #2 $182.45   7.790%   $196.6629   $196.66   $196.65   $196.70  
  Purchase #3 $73.67   11.852%   $82.4014   $82.40   $82.40   $82.40  
  Purchase #4 $241.59   13.340%   $273.8181   $273.82   $273.80   $273.80  
  Purchase #5 $159.69   11.820%   $178.5654   $178.57   $178.55   $178.60  
  Purchase #6 $131.46   12.261%   $147.5783   $147.58   $147.60   $147.60  
  Purchase #7 $153.30   3.754%   $159.0549   $159.05   $159.05   $159.10  
  7 purchase totals = $1,098.04       $1,201.2733   $1,201.27   $1,201.25   $1,201.40