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	$155.98	6.185%	$165.6274	$165.63	$165.65	$165.60
Purchase #2	$82.96	3.107%	$85.5376	$85.54	$85.55	$85.50
Purchase #3	$58.30	12.557%	$65.6207	$65.62	$65.60	$65.60
Purchase #4	$62.52	6.339%	$66.4831	$66.48	$66.50	$66.50
Purchase #5	$89.77	12.242%	$100.7596	$100.76	$100.75	$100.80
Purchase #6	$83.62	3.650%	$86.6721	$86.67	$86.65	$86.70
Purchase #7	$246.53	5.224%	$259.4087	$259.41	$259.40	$259.40
7 purchase totals =	$779.68		$830.1092	$830.11	$830.10	$830.10