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	$206.57	13.663%	$234.7937	$234.79	$234.80	$234.80
Purchase #2	$29.47	8.151%	$31.8721	$31.87	$31.85	$31.90
Purchase #3	$165.70	13.636%	$188.2949	$188.29	$188.30	$188.30
Purchase #4	$79.42	12.774%	$89.5651	$89.57	$89.55	$89.60
Purchase #5	$131.59	3.773%	$136.5549	$136.55	$136.55	$136.60
Purchase #6	$84.51	3.317%	$87.3132	$87.31	$87.30	$87.30
Purchase #7	$73.66	13.658%	$83.7205	$83.72	$83.70	$83.70
7 purchase totals =	$770.92		$852.1144	$852.10	$852.05	$852.20