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	$28.39	5.399%	$29.9228	$29.92	$29.90	$29.90
Purchase #2	$202.63	11.273%	$225.4725	$225.47	$225.45	$225.50
Purchase #3	$91.47	5.410%	$96.4185	$96.42	$96.40	$96.40
Purchase #4	$142.80	9.174%	$155.9005	$155.90	$155.90	$155.90
Purchase #5	$167.90	13.374%	$190.3549	$190.35	$190.35	$190.40
Purchase #6	$17.73	7.384%	$19.0392	$19.04	$19.05	$19.00
Purchase #7	$130.96	6.471%	$139.4344	$139.43	$139.45	$139.40
7 purchase totals =	$781.88		$856.5428	$856.53	$856.50	$856.50