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	$77.63	6.184%	$82.4306	$82.43	$82.45	$82.40
Purchase #2	$249.70	12.590%	$281.1372	$281.14	$281.15	$281.10
Purchase #3	$127.27	8.776%	$138.4392	$138.44	$138.45	$138.40
Purchase #4	$10.48	13.497%	$11.8945	$11.89	$11.90	$11.90
Purchase #5	$248.38	12.862%	$280.3266	$280.33	$280.35	$280.30
Purchase #6	$170.80	5.631%	$180.4177	$180.42	$180.40	$180.40
Purchase #7	$55.43	7.695%	$59.6953	$59.70	$59.70	$59.70
7 purchase totals =	$939.69		$1,034.3411	$1,034.35	$1,034.40	$1,034.20