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	$85.57	6.501%	$91.1329	$91.13	$91.15	$91.10
Purchase #2	$104.78	4.535%	$109.5318	$109.53	$109.55	$109.50
Purchase #3	$27.44	3.780%	$28.4772	$28.48	$28.50	$28.50
Purchase #4	$76.42	8.125%	$82.6291	$82.63	$82.65	$82.60
Purchase #5	$55.88	9.631%	$61.2618	$61.26	$61.25	$61.30
Purchase #6	$28.37	12.319%	$31.8649	$31.86	$31.85	$31.90
Purchase #7	$211.58	8.378%	$229.3062	$229.31	$229.30	$229.30
7 purchase totals =	$590.04		$634.2039	$634.20	$634.25	$634.20