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 $144.87   5.841%   $153.3319   $153.33   $153.35   $153.30  
  Purchase #2 $197.93   12.450%   $222.5723   $222.57   $222.55   $222.60  
  Purchase #3 $96.66   5.810%   $102.2759   $102.28   $102.30   $102.30  
  Purchase #4 $32.48   7.380%   $34.877   $34.88   $34.90   $34.90  
  Purchase #5 $221.66   8.190%   $239.814   $239.81   $239.80   $239.80  
  Purchase #6 $236.79   4.845%   $248.2625   $248.26   $248.25   $248.30  
  Purchase #7 $39.49   9.612%   $43.2858   $43.29   $43.30   $43.30  
  7 purchase totals = $969.88       $1,044.4194   $1,044.42   $1,044.45   $1,044.50