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	$182.40	3.797%	$189.3257	$189.33	$189.35	$189.30
Purchase #2	$96.98	13.167%	$109.7494	$109.75	$109.75	$109.70
Purchase #3	$46.81	8.595%	$50.8333	$50.83	$50.85	$50.80
Purchase #4	$74.42	11.168%	$82.7312	$82.73	$82.75	$82.70
Purchase #5	$175.68	12.790%	$198.1495	$198.15	$198.15	$198.10
Purchase #6	$50.57	4.470%	$52.8305	$52.83	$52.85	$52.80
Purchase #7	$99.30	8.366%	$107.6074	$107.61	$107.60	$107.60
7 purchase totals =	$726.16		$791.2270	$791.23	$791.30	$791.00