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	$54.59	4.267%	$56.9194	$56.92	$56.90	$56.90
Purchase #2	$30.37	9.127%	$33.1419	$33.14	$33.15	$33.10
Purchase #3	$221.45	11.401%	$246.6975	$246.70	$246.70	$246.70
Purchase #4	$103.86	5.751%	$109.833	$109.83	$109.85	$109.80
Purchase #5	$244.53	11.776%	$273.3259	$273.33	$273.35	$273.30
Purchase #6	$223.54	7.562%	$240.4441	$240.44	$240.45	$240.40
Purchase #7	$209.72	6.386%	$223.1127	$223.11	$223.10	$223.10
7 purchase totals =	$1,088.06		$1,183.4745	$1,183.47	$1,183.50	$1,183.30