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	$156.51	10.766%	$173.3599	$173.36	$173.35	$173.40
Purchase #2	$61.72	3.401%	$63.8191	$63.82	$63.80	$63.80
Purchase #3	$109.62	12.704%	$123.5461	$123.55	$123.55	$123.50
Purchase #4	$243.90	8.194%	$263.8852	$263.89	$263.90	$263.90
Purchase #5	$232.33	9.114%	$253.5046	$253.50	$253.50	$253.50
Purchase #6	$36.79	10.413%	$40.6209	$40.62	$40.60	$40.60
Purchase #7	$82.35	11.298%	$91.6539	$91.65	$91.65	$91.70
7 purchase totals =	$923.22		$1,010.3897	$1,010.39	$1,010.35	$1,010.40