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	$45.43	3.240%	$46.9019	$46.90	$46.90	$46.90
Purchase #2	$225.83	13.700%	$256.7687	$256.77	$256.75	$256.80
Purchase #3	$128.38	12.472%	$144.3916	$144.39	$144.40	$144.40
Purchase #4	$237.40	13.214%	$268.77	$268.77	$268.75	$268.80
Purchase #5	$174.89	9.699%	$191.8526	$191.85	$191.85	$191.90
Purchase #6	$133.73	5.712%	$141.3687	$141.37	$141.35	$141.40
Purchase #7	$145.93	7.633%	$157.0688	$157.07	$157.05	$157.10
7 purchase totals =	$1,091.59		$1,207.1223	$1,207.12	$1,207.05	$1,207.30