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	$48.96	12.162%	$54.9145	$54.91	$54.90	$54.90
Purchase #2	$139.53	10.285%	$153.8807	$153.88	$153.90	$153.90
Purchase #3	$205.37	11.553%	$229.0964	$229.10	$229.10	$229.10
Purchase #4	$219.65	10.788%	$243.3458	$243.35	$243.35	$243.30
Purchase #5	$103.51	11.633%	$115.5513	$115.55	$115.55	$115.60
Purchase #6	$250.71	5.348%	$264.118	$264.12	$264.10	$264.10
Purchase #7	$48.66	11.628%	$54.3182	$54.32	$54.30	$54.30
7 purchase totals =	$1,016.39		$1,115.2249	$1,115.23	$1,115.20	$1,115.20