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	$163.74	5.599%	$172.9078	$172.91	$172.90	$172.90
Purchase #2	$167.65	8.792%	$182.3898	$182.39	$182.40	$182.40
Purchase #3	$221.49	7.768%	$238.6953	$238.70	$238.70	$238.70
Purchase #4	$32.82	7.349%	$35.2319	$35.23	$35.25	$35.20
Purchase #5	$61.78	9.263%	$67.5027	$67.50	$67.50	$67.50
Purchase #6	$211.43	10.840%	$234.349	$234.35	$234.35	$234.30
Purchase #7	$69.83	3.566%	$72.3201	$72.32	$72.30	$72.30
7 purchase totals =	$928.74		$1,003.3966	$1,003.40	$1,003.40	$1,003.30