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	$171.79	6.107%	$182.2812	$182.28	$182.30	$182.30
Purchase #2	$5.44	11.582%	$6.0701	$6.07	$6.05	$6.10
Purchase #3	$134.58	8.739%	$146.3409	$146.34	$146.35	$146.30
Purchase #4	$113.46	9.186%	$123.8824	$123.88	$123.90	$123.90
Purchase #5	$213.98	4.643%	$223.9151	$223.92	$223.90	$223.90
Purchase #6	$93.29	7.854%	$100.617	$100.62	$100.60	$100.60
Purchase #7	$136.94	13.199%	$155.0147	$155.01	$155.00	$155.00
7 purchase totals =	$869.48		$938.1214	$938.12	$938.10	$938.10