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	$190.36	11.484%	$212.2209	$212.22	$212.20	$212.20
Purchase #2	$32.90	4.865%	$34.5006	$34.50	$34.50	$34.50
Purchase #3	$96.71	3.309%	$99.9101	$99.91	$99.90	$99.90
Purchase #4	$25.48	7.720%	$27.4471	$27.45	$27.45	$27.40
Purchase #5	$225.64	11.158%	$250.8169	$250.82	$250.80	$250.80
Purchase #6	$171.45	11.568%	$191.2833	$191.28	$191.30	$191.30
Purchase #7	$76.57	6.700%	$81.7002	$81.70	$81.70	$81.70
7 purchase totals =	$819.11		$897.8791	$897.88	$897.85	$897.80