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	$169.39	11.692%	$189.1951	$189.20	$189.20	$189.20
Purchase #2	$82.69	8.128%	$89.411	$89.41	$89.40	$89.40
Purchase #3	$13.26	4.754%	$13.8904	$13.89	$13.90	$13.90
Purchase #4	$249.87	13.816%	$284.392	$284.39	$284.40	$284.40
Purchase #5	$169.36	12.289%	$190.1727	$190.17	$190.15	$190.20
Purchase #6	$59.32	6.706%	$63.298	$63.30	$63.30	$63.30
Purchase #7	$129.54	10.684%	$143.3801	$143.38	$143.40	$143.40
7 purchase totals =	$873.43		$973.7393	$973.74	$973.75	$973.80