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	$78.87	3.422%	$81.5689	$81.57	$81.55	$81.60
Purchase #2	$79.67	5.334%	$83.9196	$83.92	$83.90	$83.90
Purchase #3	$79.33	12.752%	$89.4462	$89.45	$89.45	$89.40
Purchase #4	$194.56	4.689%	$203.6829	$203.68	$203.70	$203.70
Purchase #5	$96.51	6.194%	$102.4878	$102.49	$102.50	$102.50
Purchase #6	$179.35	11.866%	$200.6317	$200.63	$200.65	$200.60
Purchase #7	$83.71	5.374%	$88.2086	$88.21	$88.20	$88.20
7 purchase totals =	$792.00		$849.9457	$849.95	$849.95	$849.90