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	$169.81	11.272%	$188.951	$188.95	$188.95	$189.00
Purchase #2	$74.64	7.217%	$80.0268	$80.03	$80.05	$80.00
Purchase #3	$38.33	11.158%	$42.6069	$42.61	$42.60	$42.60
Purchase #4	$73.63	11.526%	$82.1166	$82.12	$82.10	$82.10
Purchase #5	$65.78	5.119%	$69.1473	$69.15	$69.15	$69.10
Purchase #6	$226.76	6.727%	$242.0141	$242.01	$242.00	$242.00
Purchase #7	$118.56	11.729%	$132.4659	$132.47	$132.45	$132.50
7 purchase totals =	$767.51		$837.3286	$837.34	$837.30	$837.30