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	$249.85	9.290%	$273.0611	$273.06	$273.05	$273.10
Purchase #2	$80.99	9.748%	$88.8849	$88.88	$88.90	$88.90
Purchase #3	$31.76	4.769%	$33.2746	$33.27	$33.25	$33.30
Purchase #4	$76.36	8.574%	$82.9071	$82.91	$82.90	$82.90
Purchase #5	$246.72	12.703%	$278.0608	$278.06	$278.05	$278.10
Purchase #6	$240.99	3.333%	$249.0222	$249.02	$249.00	$249.00
Purchase #7	$90.66	4.360%	$94.6128	$94.61	$94.60	$94.60
7 purchase totals =	$1,017.33		$1,099.8235	$1,099.81	$1,099.75	$1,099.90