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	$88.71	11.205%	$98.65	$98.65	$98.65	$98.70
Purchase #2	$174.57	4.340%	$182.1463	$182.15	$182.15	$182.10
Purchase #3	$122.34	7.194%	$131.1411	$131.14	$131.15	$131.10
Purchase #4	$69.56	4.293%	$72.5462	$72.55	$72.55	$72.50
Purchase #5	$101.86	7.843%	$109.8489	$109.85	$109.85	$109.80
Purchase #6	$41.92	5.815%	$44.3576	$44.36	$44.35	$44.40
Purchase #7	$237.65	7.420%	$255.2836	$255.28	$255.30	$255.30
7 purchase totals =	$836.61		$893.9737	$893.98	$894.00	$893.90