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	$133.39	4.279%	$139.0978	$139.10	$139.10	$139.10
Purchase #2	$174.44	3.744%	$180.971	$180.97	$180.95	$181.00
Purchase #3	$88.62	13.225%	$100.34	$100.34	$100.35	$100.30
Purchase #4	$130.89	8.378%	$141.856	$141.86	$141.85	$141.90
Purchase #5	$125.43	4.674%	$131.2926	$131.29	$131.30	$131.30
Purchase #6	$172.62	4.589%	$180.5415	$180.54	$180.55	$180.50
Purchase #7	$73.87	3.739%	$76.632	$76.63	$76.65	$76.60
7 purchase totals =	$899.26		$950.7309	$950.73	$950.75	$950.70