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	$67.89	6.617%	$72.3823	$72.38	$72.40	$72.40
Purchase #2	$138.79	3.170%	$143.1896	$143.19	$143.20	$143.20
Purchase #3	$92.90	6.610%	$99.0407	$99.04	$99.05	$99.00
Purchase #4	$70.92	11.792%	$79.2829	$79.28	$79.30	$79.30
Purchase #5	$82.69	13.681%	$94.0028	$94.00	$94.00	$94.00
Purchase #6	$82.81	10.437%	$91.4529	$91.45	$91.45	$91.50
Purchase #7	$157.39	6.345%	$167.3764	$167.38	$167.40	$167.40
7 purchase totals =	$693.39		$746.7276	$746.72	$746.80	$746.80