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	$245.67	11.679%	$274.3618	$274.36	$274.35	$274.40
Purchase #2	$57.66	12.610%	$64.9309	$64.93	$64.95	$64.90
Purchase #3	$152.34	6.304%	$161.9435	$161.94	$161.95	$161.90
Purchase #4	$212.92	12.199%	$238.8941	$238.89	$238.90	$238.90
Purchase #5	$65.34	5.681%	$69.052	$69.05	$69.05	$69.10
Purchase #6	$31.38	4.231%	$32.7077	$32.71	$32.70	$32.70
Purchase #7	$107.90	3.430%	$111.601	$111.60	$111.60	$111.60
7 purchase totals =	$873.21		$953.4910	$953.48	$953.50	$953.50