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	$35.64	6.231%	$37.8607	$37.86	$37.85	$37.90
Purchase #2	$126.82	8.765%	$137.9358	$137.94	$137.95	$137.90
Purchase #3	$106.34	7.803%	$114.6377	$114.64	$114.65	$114.60
Purchase #4	$93.45	12.678%	$105.2976	$105.30	$105.30	$105.30
Purchase #5	$219.81	11.455%	$244.9892	$244.99	$245.00	$245.00
Purchase #6	$98.63	10.746%	$109.2288	$109.23	$109.25	$109.20
Purchase #7	$74.82	13.735%	$85.0965	$85.10	$85.10	$85.10
7 purchase totals =	$755.51		$835.0463	$835.06	$835.10	$835.00