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	$162.80	3.383%	$168.3075	$168.31	$168.30	$168.30
Purchase #2	$47.41	8.541%	$51.4593	$51.46	$51.45	$51.50
Purchase #3	$196.34	11.306%	$218.5382	$218.54	$218.55	$218.50
Purchase #4	$106.81	11.362%	$118.9458	$118.95	$118.95	$118.90
Purchase #5	$154.39	11.836%	$172.6636	$172.66	$172.65	$172.70
Purchase #6	$26.71	7.228%	$28.6406	$28.64	$28.65	$28.60
Purchase #7	$83.64	6.109%	$88.7496	$88.75	$88.75	$88.70
7 purchase totals =	$778.10		$847.3046	$847.31	$847.30	$847.20