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 $237.28   13.654%   $269.6782   $269.68   $269.70   $269.70  
  Purchase #2 $105.39   13.466%   $119.5818   $119.58   $119.60   $119.60  
  Purchase #3 $70.31   12.612%   $79.1775   $79.18   $79.20   $79.20  
  Purchase #4 $71.26   12.275%   $80.0072   $80.01   $80.00   $80.00  
  Purchase #5 $240.98   4.794%   $252.5326   $252.53   $252.55   $252.50  
  Purchase #6 $140.88   8.537%   $152.9069   $152.91   $152.90   $152.90  
  Purchase #7 $116.25   3.445%   $120.2548   $120.25   $120.25   $120.30  
  7 purchase totals = $982.35       $1,074.1390   $1,074.14   $1,074.20   $1,074.20