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 $168.98   8.714%   $183.7049   $183.70   $183.70   $183.70  
  Purchase #2 $195.79   3.787%   $203.2046   $203.20   $203.20   $203.20  
  Purchase #3 $184.44   6.822%   $197.0225   $197.02   $197.00   $197.00  
  Purchase #4 $43.46   9.509%   $47.5926   $47.59   $47.60   $47.60  
  Purchase #5 $66.70   5.299%   $70.2344   $70.23   $70.25   $70.20  
  Purchase #6 $241.51   5.131%   $253.9019   $253.90   $253.90   $253.90  
  Purchase #7 $157.51   9.686%   $172.7664   $172.77   $172.75   $172.80  
  7 purchase totals = $1,058.39       $1,128.4273   $1,128.41   $1,128.40   $1,128.40