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	$207.55	4.163%	$216.1903	$216.19	$216.20	$216.20
Purchase #2	$71.77	8.458%	$77.8403	$77.84	$77.85	$77.80
Purchase #3	$77.71	11.518%	$86.6606	$86.66	$86.65	$86.70
Purchase #4	$78.75	13.215%	$89.1568	$89.16	$89.15	$89.20
Purchase #5	$92.47	8.257%	$100.1052	$100.11	$100.10	$100.10
Purchase #6	$52.36	12.754%	$59.038	$59.04	$59.05	$59.00
Purchase #7	$147.50	11.793%	$164.8947	$164.89	$164.90	$164.90
7 purchase totals =	$728.11		$793.8859	$793.89	$793.90	$793.90