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	$246.83	11.402%	$274.9736	$274.97	$274.95	$275.00
Purchase #2	$103.64	13.153%	$117.2718	$117.27	$117.25	$117.30
Purchase #3	$136.88	6.352%	$145.5746	$145.57	$145.55	$145.60
Purchase #4	$139.46	13.305%	$158.0152	$158.02	$158.00	$158.00
Purchase #5	$45.76	11.537%	$51.0393	$51.04	$51.05	$51.00
Purchase #6	$35.50	8.146%	$38.3918	$38.39	$38.40	$38.40
Purchase #7	$64.79	11.337%	$72.1352	$72.14	$72.15	$72.10
7 purchase totals =	$772.86		$857.4015	$857.40	$857.35	$857.40