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	$52.89	6.821%	$56.4976	$56.50	$56.50	$56.50
Purchase #2	$39.96	8.212%	$43.2415	$43.24	$43.25	$43.20
Purchase #3	$223.57	13.164%	$253.0008	$253.00	$253.00	$253.00
Purchase #4	$93.82	10.224%	$103.4122	$103.41	$103.40	$103.40
Purchase #5	$53.40	8.579%	$57.9812	$57.98	$58.00	$58.00
Purchase #6	$86.64	10.816%	$96.011	$96.01	$96.00	$96.00
Purchase #7	$198.28	8.600%	$215.3321	$215.33	$215.35	$215.30
7 purchase totals =	$748.56		$825.4764	$825.47	$825.50	$825.40