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	$108.53	13.366%	$123.0361	$123.04	$123.05	$123.00
Purchase #2	$166.74	3.319%	$172.2741	$172.27	$172.25	$172.30
Purchase #3	$170.76	12.179%	$191.5569	$191.56	$191.55	$191.60
Purchase #4	$67.74	6.133%	$71.8945	$71.89	$71.90	$71.90
Purchase #5	$20.99	8.463%	$22.7664	$22.77	$22.75	$22.80
Purchase #6	$109.37	6.258%	$116.2144	$116.21	$116.20	$116.20
Purchase #7	$109.86	11.497%	$122.4906	$122.49	$122.50	$122.50
7 purchase totals =	$753.99		$820.2330	$820.23	$820.20	$820.30