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	$31.49	5.607%	$33.2556	$33.26	$33.25	$33.30
Purchase #2	$94.72	13.569%	$107.5726	$107.57	$107.55	$107.60
Purchase #3	$236.48	9.472%	$258.8794	$258.88	$258.90	$258.90
Purchase #4	$88.37	13.192%	$100.0278	$100.03	$100.05	$100.00
Purchase #5	$240.41	11.360%	$267.7206	$267.72	$267.70	$267.70
Purchase #6	$206.69	7.589%	$222.3757	$222.38	$222.40	$222.40
Purchase #7	$131.44	12.346%	$147.6676	$147.67	$147.65	$147.70
7 purchase totals =	$1,029.60		$1,137.4993	$1,137.51	$1,137.50	$1,137.60