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	$79.31	3.741%	$82.277	$82.28	$82.30	$82.30
Purchase #2	$156.91	13.671%	$178.3612	$178.36	$178.35	$178.40
Purchase #3	$47.57	11.658%	$53.1157	$53.12	$53.10	$53.10
Purchase #4	$59.57	11.642%	$66.5051	$66.51	$66.50	$66.50
Purchase #5	$46.25	9.351%	$50.5748	$50.57	$50.55	$50.60
Purchase #6	$218.71	12.270%	$245.5457	$245.55	$245.55	$245.50
Purchase #7	$111.71	13.280%	$126.5451	$126.55	$126.55	$126.50
7 purchase totals =	$720.03		$802.9246	$802.94	$802.90	$802.90