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 $61.98   12.434%   $69.6866   $69.69   $69.70   $69.70  
  Purchase #2 $111.79   6.681%   $119.2587   $119.26   $119.25   $119.30  
  Purchase #3 $38.28   9.243%   $41.8182   $41.82   $41.80   $41.80  
  Purchase #4 $54.82   10.183%   $60.4023   $60.40   $60.40   $60.40  
  Purchase #5 $128.75   5.324%   $135.6047   $135.60   $135.60   $135.60  
  Purchase #6 $74.31   12.653%   $83.7124   $83.71   $83.70   $83.70  
  Purchase #7 $172.54   7.673%   $185.779   $185.78   $185.80   $185.80  
  7 purchase totals = $642.47       $696.2619   $696.26   $696.25   $696.30