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 $141.56   3.696%   $146.7921   $146.79   $146.80   $146.80  
  Purchase #2 $32.81   6.667%   $34.9974   $35.00   $35.00   $35.00  
  Purchase #3 $56.94   13.361%   $64.5478   $64.55   $64.55   $64.50  
  Purchase #4 $221.85   11.102%   $246.4798   $246.48   $246.50   $246.50  
  Purchase #5 $200.80   13.368%   $227.6429   $227.64   $227.65   $227.60  
  Purchase #6 $120.44   8.155%   $130.2619   $130.26   $130.25   $130.30  
  Purchase #7 $245.80   11.298%   $273.5705   $273.57   $273.55   $273.60  
  7 purchase totals = $1,020.20       $1,124.2924   $1,124.29   $1,124.30   $1,124.30