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	$223.96	11.633%	$250.0133	$250.01	$250.00	$250.00
Purchase #2	$78.61	7.217%	$84.2833	$84.28	$84.30	$84.30
Purchase #3	$166.30	3.379%	$171.9193	$171.92	$171.90	$171.90
Purchase #4	$44.78	3.538%	$46.3643	$46.36	$46.35	$46.40
Purchase #5	$154.96	10.640%	$171.4477	$171.45	$171.45	$171.40
Purchase #6	$43.38	3.821%	$45.0375	$45.04	$45.05	$45.00
Purchase #7	$67.89	8.637%	$73.7537	$73.75	$73.75	$73.80
7 purchase totals =	$779.88		$842.8191	$842.81	$842.80	$842.80