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	$70.56	11.438%	$78.6307	$78.63	$78.65	$78.60
Purchase #2	$94.38	7.345%	$101.3122	$101.31	$101.30	$101.30
Purchase #3	$70.95	9.843%	$77.9336	$77.93	$77.95	$77.90
Purchase #4	$108.56	11.336%	$120.8664	$120.87	$120.85	$120.90
Purchase #5	$37.71	7.769%	$40.6397	$40.64	$40.65	$40.60
Purchase #6	$53.54	11.402%	$59.6446	$59.64	$59.65	$59.60
Purchase #7	$63.64	13.620%	$72.3078	$72.31	$72.30	$72.30
7 purchase totals =	$499.34		$551.3350	$551.33	$551.35	$551.20