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	$101.32	8.579%	$110.0122	$110.01	$110.00	$110.00
Purchase #2	$60.73	6.753%	$64.8311	$64.83	$64.85	$64.80
Purchase #3	$36.85	6.583%	$39.2758	$39.28	$39.30	$39.30
Purchase #4	$221.31	3.620%	$229.3214	$229.32	$229.30	$229.30
Purchase #5	$27.43	3.134%	$28.2897	$28.29	$28.30	$28.30
Purchase #6	$95.28	9.485%	$104.3173	$104.32	$104.30	$104.30
Purchase #7	$185.43	8.334%	$200.8837	$200.88	$200.90	$200.90
7 purchase totals =	$728.35		$776.9312	$776.93	$776.95	$776.90