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	$20.40	6.814%	$21.7901	$21.79	$21.80	$21.80
Purchase #2	$171.54	11.411%	$191.1144	$191.11	$191.10	$191.10
Purchase #3	$181.63	12.768%	$204.8205	$204.82	$204.80	$204.80
Purchase #4	$98.97	6.170%	$105.0764	$105.08	$105.10	$105.10
Purchase #5	$89.77	9.820%	$98.5854	$98.59	$98.60	$98.60
Purchase #6	$51.86	11.202%	$57.6694	$57.67	$57.65	$57.70
Purchase #7	$86.88	5.705%	$91.8365	$91.84	$91.85	$91.80
7 purchase totals =	$701.05		$770.8927	$770.90	$770.90	$770.90