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	$128.91	5.656%	$136.2011	$136.20	$136.20	$136.20
Purchase #2	$109.54	12.543%	$123.2796	$123.28	$123.30	$123.30
Purchase #3	$64.67	3.817%	$67.1385	$67.14	$67.15	$67.10
Purchase #4	$159.76	4.745%	$167.3406	$167.34	$167.35	$167.30
Purchase #5	$24.73	11.201%	$27.5	$27.50	$27.50	$27.50
Purchase #6	$226.95	10.215%	$250.1329	$250.13	$250.15	$250.10
Purchase #7	$174.95	8.274%	$189.4254	$189.43	$189.45	$189.40
7 purchase totals =	$889.51		$961.0181	$961.02	$961.10	$960.90