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	$42.73	5.719%	$45.1737	$45.17	$45.15	$45.20
Purchase #2	$77.66	4.854%	$81.4296	$81.43	$81.45	$81.40
Purchase #3	$72.46	12.216%	$81.3117	$81.31	$81.30	$81.30
Purchase #4	$57.87	12.111%	$64.8786	$64.88	$64.90	$64.90
Purchase #5	$99.30	12.687%	$111.8982	$111.90	$111.90	$111.90
Purchase #6	$227.90	6.478%	$242.6634	$242.66	$242.65	$242.70
Purchase #7	$195.90	3.515%	$202.7859	$202.79	$202.80	$202.80
7 purchase totals =	$773.82		$830.1411	$830.14	$830.15	$830.20