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	$6.83	6.370%	$7.2651	$7.27	$7.25	$7.30
Purchase #2	$92.70	7.231%	$99.4031	$99.40	$99.40	$99.40
Purchase #3	$55.76	13.785%	$63.4465	$63.45	$63.45	$63.40
Purchase #4	$156.83	3.172%	$161.8046	$161.80	$161.80	$161.80
Purchase #5	$84.93	13.340%	$96.2597	$96.26	$96.25	$96.30
Purchase #6	$42.98	10.153%	$47.3438	$47.34	$47.35	$47.30
Purchase #7	$85.91	10.292%	$94.7519	$94.75	$94.75	$94.80
7 purchase totals =	$525.94		$570.2747	$570.27	$570.25	$570.30