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	$42.72	5.578%	$45.1029	$45.10	$45.10	$45.10
Purchase #2	$116.57	7.870%	$125.7441	$125.74	$125.75	$125.70
Purchase #3	$127.83	9.858%	$140.4315	$140.43	$140.45	$140.40
Purchase #4	$180.39	5.287%	$189.9272	$189.93	$189.95	$189.90
Purchase #5	$250.88	7.479%	$269.6433	$269.64	$269.65	$269.60
Purchase #6	$82.67	9.233%	$90.3029	$90.30	$90.30	$90.30
Purchase #7	$171.33	12.341%	$192.4738	$192.47	$192.45	$192.50
7 purchase totals =	$972.39		$1,053.6257	$1,053.61	$1,053.65	$1,053.50