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	$115.29	7.467%	$123.8987	$123.90	$123.90	$123.90
Purchase #2	$55.55	6.772%	$59.3118	$59.31	$59.30	$59.30
Purchase #3	$82.85	12.599%	$93.2883	$93.29	$93.30	$93.30
Purchase #4	$140.88	8.786%	$153.2577	$153.26	$153.25	$153.30
Purchase #5	$65.65	3.571%	$67.9944	$67.99	$68.00	$68.00
Purchase #6	$191.38	7.711%	$206.1373	$206.14	$206.15	$206.10
Purchase #7	$79.55	7.140%	$85.2299	$85.23	$85.25	$85.20
7 purchase totals =	$731.15		$789.1181	$789.12	$789.15	$789.10