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	$91.59	12.814%	$103.3263	$103.33	$103.35	$103.30
Purchase #2	$119.78	6.559%	$127.6364	$127.64	$127.65	$127.60
Purchase #3	$98.40	6.656%	$104.9495	$104.95	$104.95	$104.90
Purchase #4	$209.75	11.615%	$234.1125	$234.11	$234.10	$234.10
Purchase #5	$36.63	12.558%	$41.23	$41.23	$41.25	$41.20
Purchase #6	$63.55	13.123%	$71.8897	$71.89	$71.90	$71.90
Purchase #7	$137.61	4.827%	$144.2524	$144.25	$144.25	$144.30
7 purchase totals =	$757.31		$827.3968	$827.40	$827.45	$827.30