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	$143.80	5.250%	$151.3495	$151.35	$151.35	$151.30
Purchase #2	$79.41	8.834%	$86.4251	$86.43	$86.45	$86.40
Purchase #3	$171.73	5.143%	$180.5621	$180.56	$180.55	$180.60
Purchase #4	$105.33	6.430%	$112.1027	$112.10	$112.10	$112.10
Purchase #5	$179.35	11.744%	$200.4129	$200.41	$200.40	$200.40
Purchase #6	$73.92	12.410%	$83.0935	$83.09	$83.10	$83.10
Purchase #7	$10.40	12.234%	$11.6723	$11.67	$11.65	$11.70
7 purchase totals =	$763.94		$825.6181	$825.61	$825.60	$825.60