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	$124.73	9.331%	$136.3686	$136.37	$136.35	$136.40
Purchase #2	$81.41	12.868%	$91.8858	$91.89	$91.90	$91.90
Purchase #3	$24.73	10.102%	$27.2282	$27.23	$27.25	$27.20
Purchase #4	$147.48	3.433%	$152.543	$152.54	$152.55	$152.50
Purchase #5	$249.73	9.577%	$273.6466	$273.65	$273.65	$273.60
Purchase #6	$145.50	5.543%	$153.5651	$153.57	$153.55	$153.60
Purchase #7	$71.71	11.423%	$79.9014	$79.90	$79.90	$79.90
7 purchase totals =	$845.29		$915.1387	$915.15	$915.15	$915.10