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	$42.39	7.113%	$45.4052	$45.41	$45.40	$45.40
Purchase #2	$51.27	3.670%	$53.1516	$53.15	$53.15	$53.20
Purchase #3	$196.36	10.143%	$216.2768	$216.28	$216.30	$216.30
Purchase #4	$105.47	9.526%	$115.5171	$115.52	$115.50	$115.50
Purchase #5	$178.71	3.145%	$184.3304	$184.33	$184.35	$184.30
Purchase #6	$147.29	3.723%	$152.7736	$152.77	$152.75	$152.80
Purchase #7	$18.31	9.135%	$19.9826	$19.98	$20.00	$20.00
7 purchase totals =	$739.80		$787.4373	$787.44	$787.45	$787.50