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	$37.70	9.714%	$41.3622	$41.36	$41.35	$41.40
Purchase #2	$79.91	7.423%	$85.8417	$85.84	$85.85	$85.80
Purchase #3	$90.32	9.641%	$99.0278	$99.03	$99.05	$99.00
Purchase #4	$139.38	12.570%	$156.9001	$156.90	$156.90	$156.90
Purchase #5	$45.69	4.459%	$47.7273	$47.73	$47.75	$47.70
Purchase #6	$88.36	9.512%	$96.7648	$96.76	$96.75	$96.80
Purchase #7	$108.38	13.568%	$123.085	$123.09	$123.10	$123.10
7 purchase totals =	$589.74		$650.7089	$650.71	$650.75	$650.70