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	$38.32	4.662%	$40.1065	$40.11	$40.10	$40.10
Purchase #2	$49.27	7.442%	$52.9367	$52.94	$52.95	$52.90
Purchase #3	$203.85	12.785%	$229.9122	$229.91	$229.90	$229.90
Purchase #4	$88.40	3.296%	$91.3137	$91.31	$91.30	$91.30
Purchase #5	$155.44	10.259%	$171.3866	$171.39	$171.40	$171.40
Purchase #6	$135.86	10.684%	$150.3753	$150.38	$150.40	$150.40
Purchase #7	$79.98	5.509%	$84.3861	$84.39	$84.40	$84.40
7 purchase totals =	$751.12		$820.4171	$820.43	$820.45	$820.40