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	$81.90	11.389%	$91.2276	$91.23	$91.25	$91.20
Purchase #2	$189.61	10.476%	$209.4735	$209.47	$209.45	$209.50
Purchase #3	$123.73	13.380%	$140.2851	$140.29	$140.30	$140.30
Purchase #4	$27.77	11.679%	$31.0133	$31.01	$31.00	$31.00
Purchase #5	$180.66	5.401%	$190.4174	$190.42	$190.40	$190.40
Purchase #6	$141.71	3.772%	$147.0553	$147.06	$147.05	$147.10
Purchase #7	$73.46	6.427%	$78.1813	$78.18	$78.20	$78.20
7 purchase totals =	$818.84		$887.6535	$887.66	$887.65	$887.70