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	$46.41	9.803%	$50.9596	$50.96	$50.95	$51.00
Purchase #2	$137.55	7.334%	$147.6379	$147.64	$147.65	$147.60
Purchase #3	$76.53	11.245%	$85.1358	$85.14	$85.15	$85.10
Purchase #4	$122.45	7.405%	$131.5174	$131.52	$131.50	$131.50
Purchase #5	$168.95	12.710%	$190.4235	$190.42	$190.40	$190.40
Purchase #6	$76.31	3.705%	$79.1373	$79.14	$79.15	$79.10
Purchase #7	$220.85	11.472%	$246.1859	$246.19	$246.20	$246.20
7 purchase totals =	$849.05		$930.9974	$931.01	$931.00	$930.90