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	$55.91	3.478%	$57.8545	$57.85	$57.85	$57.90
Purchase #2	$37.86	7.121%	$40.556	$40.56	$40.55	$40.60
Purchase #3	$15.95	6.740%	$17.025	$17.03	$17.05	$17.00
Purchase #4	$81.43	6.109%	$86.4046	$86.40	$86.40	$86.40
Purchase #5	$12.41	6.799%	$13.2538	$13.25	$13.25	$13.30
Purchase #6	$242.67	3.163%	$250.3457	$250.35	$250.35	$250.30
Purchase #7	$57.43	13.800%	$65.3553	$65.36	$65.35	$65.40
7 purchase totals =	$503.66		$530.7949	$530.80	$530.80	$530.90