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	$97.56	13.306%	$110.5413	$110.54	$110.55	$110.50
Purchase #2	$205.38	3.302%	$212.1616	$212.16	$212.15	$212.20
Purchase #3	$101.71	7.331%	$109.1664	$109.17	$109.15	$109.20
Purchase #4	$209.86	6.411%	$223.3141	$223.31	$223.30	$223.30
Purchase #5	$162.63	10.149%	$179.1353	$179.14	$179.15	$179.10
Purchase #6	$82.75	3.737%	$85.8424	$85.84	$85.85	$85.80
Purchase #7	$17.42	7.154%	$18.6662	$18.67	$18.65	$18.70
7 purchase totals =	$877.31		$938.8273	$938.83	$938.80	$938.80