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	$79.52	13.852%	$90.5351	$90.54	$90.55	$90.50
Purchase #2	$242.55	7.218%	$260.0573	$260.06	$260.05	$260.10
Purchase #3	$211.26	13.731%	$240.2681	$240.27	$240.25	$240.30
Purchase #4	$149.41	6.642%	$159.3338	$159.33	$159.35	$159.30
Purchase #5	$28.51	11.674%	$31.8383	$31.84	$31.85	$31.80
Purchase #6	$231.72	6.180%	$246.0403	$246.04	$246.05	$246.00
Purchase #7	$111.39	7.363%	$119.5916	$119.59	$119.60	$119.60
7 purchase totals =	$1,054.36		$1,147.6645	$1,147.67	$1,147.70	$1,147.60