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	$35.30	10.372%	$38.9613	$38.96	$38.95	$39.00
Purchase #2	$170.85	13.191%	$193.3868	$193.39	$193.40	$193.40
Purchase #3	$199.63	11.330%	$222.2481	$222.25	$222.25	$222.20
Purchase #4	$77.36	5.494%	$81.6102	$81.61	$81.60	$81.60
Purchase #5	$240.73	11.684%	$268.8569	$268.86	$268.85	$268.90
Purchase #6	$165.46	12.785%	$186.6141	$186.61	$186.60	$186.60
Purchase #7	$187.69	4.752%	$196.609	$196.61	$196.60	$196.60
7 purchase totals =	$1,077.02		$1,188.2864	$1,188.29	$1,188.25	$1,188.30