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	$57.33	3.472%	$59.3205	$59.32	$59.30	$59.30
Purchase #2	$140.53	6.749%	$150.0144	$150.01	$150.00	$150.00
Purchase #3	$221.47	7.400%	$237.8588	$237.86	$237.85	$237.90
Purchase #4	$84.62	6.479%	$90.1025	$90.10	$90.10	$90.10
Purchase #5	$129.93	13.670%	$147.6914	$147.69	$147.70	$147.70
Purchase #6	$157.38	7.798%	$169.6525	$169.65	$169.65	$169.70
Purchase #7	$80.59	11.163%	$89.5863	$89.59	$89.60	$89.60
7 purchase totals =	$871.85		$944.2264	$944.22	$944.20	$944.30