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	$93.45	6.277%	$99.3159	$99.32	$99.30	$99.30
Purchase #2	$122.78	4.604%	$128.4328	$128.43	$128.45	$128.40
Purchase #3	$217.59	8.266%	$235.576	$235.58	$235.60	$235.60
Purchase #4	$196.62	12.319%	$220.8416	$220.84	$220.85	$220.80
Purchase #5	$68.90	3.566%	$71.357	$71.36	$71.35	$71.40
Purchase #6	$73.60	6.573%	$78.4377	$78.44	$78.45	$78.40
Purchase #7	$78.95	13.377%	$89.5111	$89.51	$89.50	$89.50
7 purchase totals =	$851.89		$923.4721	$923.48	$923.50	$923.40