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	$127.76	11.751%	$142.7731	$142.77	$142.75	$142.80
Purchase #2	$131.50	11.818%	$147.0407	$147.04	$147.05	$147.00
Purchase #3	$20.62	13.179%	$23.3375	$23.34	$23.35	$23.30
Purchase #4	$234.29	4.547%	$244.9432	$244.94	$244.95	$244.90
Purchase #5	$77.64	4.212%	$80.9102	$80.91	$80.90	$80.90
Purchase #6	$159.96	8.820%	$174.0685	$174.07	$174.05	$174.10
Purchase #7	$82.50	8.664%	$89.6478	$89.65	$89.65	$89.60
7 purchase totals =	$834.27		$902.7210	$902.72	$902.70	$902.60