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	$33.55	5.329%	$35.3379	$35.34	$35.35	$35.30
Purchase #2	$172.68	10.148%	$190.2036	$190.20	$190.20	$190.20
Purchase #3	$50.59	7.426%	$54.3468	$54.35	$54.35	$54.30
Purchase #4	$147.73	12.295%	$165.8934	$165.89	$165.90	$165.90
Purchase #5	$200.47	12.738%	$226.0059	$226.01	$226.00	$226.00
Purchase #6	$72.52	6.531%	$77.2563	$77.26	$77.25	$77.30
Purchase #7	$86.57	3.292%	$89.4199	$89.42	$89.40	$89.40
7 purchase totals =	$764.11		$838.4638	$838.47	$838.45	$838.40