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	$163.70	6.515%	$174.3651	$174.37	$174.35	$174.40
Purchase #2	$113.76	8.352%	$123.2612	$123.26	$123.25	$123.30
Purchase #3	$85.75	6.533%	$91.352	$91.35	$91.35	$91.40
Purchase #4	$94.31	11.519%	$105.1736	$105.17	$105.15	$105.20
Purchase #5	$38.82	11.759%	$43.3848	$43.38	$43.40	$43.40
Purchase #6	$40.39	7.217%	$43.3049	$43.30	$43.30	$43.30
Purchase #7	$55.28	11.241%	$61.494	$61.49	$61.50	$61.50
7 purchase totals =	$592.01		$642.3356	$642.32	$642.30	$642.50