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	$94.31	5.618%	$99.6083	$99.61	$99.60	$99.60
Purchase #2	$199.61	9.511%	$218.5949	$218.59	$218.60	$218.60
Purchase #3	$120.29	9.522%	$131.744	$131.74	$131.75	$131.70
Purchase #4	$87.64	9.414%	$95.8904	$95.89	$95.90	$95.90
Purchase #5	$35.55	12.281%	$39.9159	$39.92	$39.90	$39.90
Purchase #6	$143.90	8.829%	$156.6049	$156.60	$156.60	$156.60
Purchase #7	$213.42	10.654%	$236.1578	$236.16	$236.15	$236.20
7 purchase totals =	$894.72		$978.5162	$978.51	$978.50	$978.50