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	$185.90	13.447%	$210.898	$210.90	$210.90	$210.90
Purchase #2	$194.91	11.241%	$216.8198	$216.82	$216.80	$216.80
Purchase #3	$212.72	12.143%	$238.5506	$238.55	$238.55	$238.60
Purchase #4	$35.61	11.744%	$39.792	$39.79	$39.80	$39.80
Purchase #5	$96.30	13.294%	$109.1021	$109.10	$109.10	$109.10
Purchase #6	$28.72	5.494%	$30.2979	$30.30	$30.30	$30.30
Purchase #7	$51.57	3.493%	$53.3713	$53.37	$53.35	$53.40
7 purchase totals =	$805.73		$898.8317	$898.83	$898.80	$898.90