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	$36.57	3.201%	$37.7406	$37.74	$37.75	$37.70
Purchase #2	$84.79	11.328%	$94.395	$94.40	$94.40	$94.40
Purchase #3	$96.61	13.734%	$109.8784	$109.88	$109.90	$109.90
Purchase #4	$37.57	6.864%	$40.1488	$40.15	$40.15	$40.10
Purchase #5	$111.26	12.217%	$124.8526	$124.85	$124.85	$124.90
Purchase #6	$234.27	8.819%	$254.9303	$254.93	$254.95	$254.90
Purchase #7	$222.32	7.287%	$238.5205	$238.52	$238.50	$238.50
7 purchase totals =	$823.39		$900.4662	$900.47	$900.50	$900.40