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	$136.45	8.861%	$148.5408	$148.54	$148.55	$148.50
Purchase #2	$213.89	12.471%	$240.5642	$240.56	$240.55	$240.60
Purchase #3	$93.53	11.700%	$104.473	$104.47	$104.45	$104.50
Purchase #4	$55.56	3.335%	$57.4129	$57.41	$57.40	$57.40
Purchase #5	$85.84	12.410%	$96.4927	$96.49	$96.50	$96.50
Purchase #6	$140.69	4.332%	$146.7847	$146.78	$146.80	$146.80
Purchase #7	$57.36	11.168%	$63.766	$63.77	$63.75	$63.80
7 purchase totals =	$783.32		$858.0343	$858.02	$858.00	$858.10