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	$123.69	5.536%	$130.5375	$130.54	$130.55	$130.50
Purchase #2	$86.36	5.350%	$90.9803	$90.98	$91.00	$91.00
Purchase #3	$84.25	5.532%	$88.9107	$88.91	$88.90	$88.90
Purchase #4	$68.59	3.290%	$70.8466	$70.85	$70.85	$70.80
Purchase #5	$45.64	11.484%	$50.8813	$50.88	$50.90	$50.90
Purchase #6	$153.81	10.473%	$169.9185	$169.92	$169.90	$169.90
Purchase #7	$61.57	9.418%	$67.3687	$67.37	$67.35	$67.40
7 purchase totals =	$623.91		$669.4436	$669.45	$669.45	$669.40