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	$47.64	9.400%	$52.1182	$52.12	$52.10	$52.10
Purchase #2	$27.86	3.782%	$28.9137	$28.91	$28.90	$28.90
Purchase #3	$139.46	4.663%	$145.963	$145.96	$145.95	$146.00
Purchase #4	$165.67	6.481%	$176.4071	$176.41	$176.40	$176.40
Purchase #5	$167.69	9.855%	$184.2158	$184.22	$184.20	$184.20
Purchase #6	$48.73	3.107%	$50.244	$50.24	$50.25	$50.20
Purchase #7	$141.56	7.404%	$152.0411	$152.04	$152.05	$152.00
7 purchase totals =	$738.61		$789.9029	$789.90	$789.85	$789.80