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	$168.48	12.723%	$189.9157	$189.92	$189.90	$189.90
Purchase #2	$170.47	13.214%	$192.9959	$193.00	$193.00	$193.00
Purchase #3	$233.61	12.200%	$262.1104	$262.11	$262.10	$262.10
Purchase #4	$43.34	10.521%	$47.8998	$47.90	$47.90	$47.90
Purchase #5	$76.82	11.351%	$85.5398	$85.54	$85.55	$85.50
Purchase #6	$60.76	4.481%	$63.4827	$63.48	$63.50	$63.50
Purchase #7	$82.86	6.816%	$88.5077	$88.51	$88.50	$88.50
7 purchase totals =	$836.34		$930.4520	$930.46	$930.45	$930.40