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	$48.71	12.478%	$54.788	$54.79	$54.80	$54.80
Purchase #2	$245.88	13.437%	$278.9189	$278.92	$278.90	$278.90
Purchase #3	$22.39	13.819%	$25.4841	$25.48	$25.50	$25.50
Purchase #4	$100.33	6.532%	$106.8836	$106.88	$106.90	$106.90
Purchase #5	$203.90	10.553%	$225.4176	$225.42	$225.40	$225.40
Purchase #6	$37.85	6.558%	$40.3322	$40.33	$40.35	$40.30
Purchase #7	$57.65	10.826%	$63.8912	$63.89	$63.90	$63.90
7 purchase totals =	$716.71		$795.7156	$795.71	$795.75	$795.70