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	$14.40	9.220%	$15.7277	$15.73	$15.75	$15.70
Purchase #2	$133.82	12.373%	$150.3775	$150.38	$150.40	$150.40
Purchase #3	$62.54	9.171%	$68.2755	$68.28	$68.30	$68.30
Purchase #4	$157.31	6.102%	$166.9091	$166.91	$166.90	$166.90
Purchase #5	$113.73	9.322%	$124.3319	$124.33	$124.35	$124.30
Purchase #6	$96.36	3.698%	$99.9234	$99.92	$99.90	$99.90
Purchase #7	$89.73	10.272%	$98.9471	$98.95	$98.95	$98.90
7 purchase totals =	$667.89		$724.4922	$724.50	$724.55	$724.40