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	$49.34	11.423%	$54.9761	$54.98	$55.00	$55.00
Purchase #2	$52.60	8.410%	$57.0237	$57.02	$57.00	$57.00
Purchase #3	$44.73	7.397%	$48.0387	$48.04	$48.05	$48.00
Purchase #4	$184.25	3.345%	$190.4132	$190.41	$190.40	$190.40
Purchase #5	$109.77	10.147%	$120.9084	$120.91	$120.90	$120.90
Purchase #6	$156.66	11.639%	$174.8937	$174.89	$174.90	$174.90
Purchase #7	$173.60	3.871%	$180.3201	$180.32	$180.30	$180.30
7 purchase totals =	$770.95		$826.5739	$826.57	$826.55	$826.50