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	$50.80	6.501%	$54.1025	$54.10	$54.10	$54.10
Purchase #2	$198.38	5.680%	$209.648	$209.65	$209.65	$209.60
Purchase #3	$52.57	5.835%	$55.6375	$55.64	$55.65	$55.60
Purchase #4	$178.53	13.764%	$203.1029	$203.10	$203.10	$203.10
Purchase #5	$250.55	10.444%	$276.7174	$276.72	$276.70	$276.70
Purchase #6	$43.90	3.444%	$45.4119	$45.41	$45.40	$45.40
Purchase #7	$78.40	13.483%	$88.9707	$88.97	$88.95	$89.00
7 purchase totals =	$853.13		$933.5909	$933.59	$933.55	$933.50