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	$75.53	5.769%	$79.8873	$79.89	$79.90	$79.90
Purchase #2	$209.67	6.718%	$223.7556	$223.76	$223.75	$223.80
Purchase #3	$160.46	9.645%	$175.9364	$175.94	$175.95	$175.90
Purchase #4	$59.98	12.401%	$67.4181	$67.42	$67.40	$67.40
Purchase #5	$147.55	13.278%	$167.1417	$167.14	$167.15	$167.10
Purchase #6	$101.83	6.558%	$108.508	$108.51	$108.50	$108.50
Purchase #7	$222.86	9.401%	$243.8111	$243.81	$243.80	$243.80
7 purchase totals =	$977.88		$1,066.4582	$1,066.47	$1,066.45	$1,066.40