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	$167.72	12.872%	$189.3089	$189.31	$189.30	$189.30
Purchase #2	$24.93	4.644%	$26.0877	$26.09	$26.10	$26.10
Purchase #3	$120.98	8.368%	$131.1036	$131.10	$131.10	$131.10
Purchase #4	$6.90	5.403%	$7.2728	$7.27	$7.25	$7.30
Purchase #5	$80.98	3.516%	$83.8273	$83.83	$83.85	$83.80
Purchase #6	$152.46	8.461%	$165.3596	$165.36	$165.35	$165.40
Purchase #7	$51.92	6.838%	$55.4703	$55.47	$55.45	$55.50
7 purchase totals =	$605.89		$658.4302	$658.43	$658.40	$658.50