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	$136.39	3.598%	$141.2973	$141.30	$141.30	$141.30
Purchase #2	$133.55	13.368%	$151.403	$151.40	$151.40	$151.40
Purchase #3	$232.41	5.706%	$245.6713	$245.67	$245.65	$245.70
Purchase #4	$87.65	13.715%	$99.6712	$99.67	$99.65	$99.70
Purchase #5	$240.55	4.179%	$250.6026	$250.60	$250.60	$250.60
Purchase #6	$10.27	9.576%	$11.2535	$11.25	$11.25	$11.30
Purchase #7	$38.79	10.483%	$42.8564	$42.86	$42.85	$42.90
7 purchase totals =	$879.61		$942.7553	$942.75	$942.70	$942.90