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	$51.49	7.401%	$55.3008	$55.30	$55.30	$55.30
Purchase #2	$170.65	5.210%	$179.5409	$179.54	$179.55	$179.50
Purchase #3	$6.85	5.838%	$7.2499	$7.25	$7.25	$7.20
Purchase #4	$106.96	6.238%	$113.6322	$113.63	$113.65	$113.60
Purchase #5	$35.48	11.872%	$39.6922	$39.69	$39.70	$39.70
Purchase #6	$100.59	5.689%	$106.3126	$106.31	$106.30	$106.30
Purchase #7	$89.38	11.325%	$99.5023	$99.50	$99.50	$99.50
7 purchase totals =	$561.40		$601.2309	$601.22	$601.25	$601.10