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	$220.39	13.294%	$249.6886	$249.69	$249.70	$249.70
Purchase #2	$230.85	5.527%	$243.6091	$243.61	$243.60	$243.60
Purchase #3	$135.40	5.529%	$142.8863	$142.89	$142.90	$142.90
Purchase #4	$83.26	5.767%	$88.0616	$88.06	$88.05	$88.10
Purchase #5	$54.72	9.495%	$59.9157	$59.92	$59.90	$59.90
Purchase #6	$179.72	11.803%	$200.9324	$200.93	$200.95	$200.90
Purchase #7	$99.41	8.382%	$107.7425	$107.74	$107.75	$107.70
7 purchase totals =	$1,003.75		$1,092.8362	$1,092.84	$1,092.85	$1,092.80