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	$31.36	4.810%	$32.8684	$32.87	$32.85	$32.90
Purchase #2	$190.61	8.306%	$206.4421	$206.44	$206.45	$206.40
Purchase #3	$28.28	12.758%	$31.888	$31.89	$31.90	$31.90
Purchase #4	$85.45	5.373%	$90.0412	$90.04	$90.05	$90.00
Purchase #5	$40.34	6.690%	$43.0387	$43.04	$43.05	$43.00
Purchase #6	$182.81	4.746%	$191.4862	$191.49	$191.50	$191.50
Purchase #7	$176.29	7.447%	$189.4183	$189.42	$189.40	$189.40
7 purchase totals =	$735.14		$785.1829	$785.19	$785.20	$785.10