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	$53.83	12.440%	$60.5265	$60.53	$60.55	$60.50
Purchase #2	$142.99	13.334%	$162.0563	$162.06	$162.05	$162.10
Purchase #3	$209.73	11.366%	$233.5679	$233.57	$233.55	$233.60
Purchase #4	$151.48	10.350%	$167.1582	$167.16	$167.15	$167.20
Purchase #5	$247.71	12.409%	$278.4483	$278.45	$278.45	$278.40
Purchase #6	$72.89	12.440%	$81.9575	$81.96	$81.95	$82.00
Purchase #7	$165.96	5.714%	$175.443	$175.44	$175.45	$175.40
7 purchase totals =	$1,044.59		$1,159.1577	$1,159.17	$1,159.15	$1,159.20