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	$170.54	11.141%	$189.5399	$189.54	$189.55	$189.50
Purchase #2	$248.58	6.365%	$264.4021	$264.40	$264.40	$264.40
Purchase #3	$39.96	12.756%	$45.0573	$45.06	$45.05	$45.10
Purchase #4	$57.97	7.794%	$62.4882	$62.49	$62.50	$62.50
Purchase #5	$104.98	12.613%	$118.2211	$118.22	$118.20	$118.20
Purchase #6	$85.76	5.415%	$90.4039	$90.40	$90.40	$90.40
Purchase #7	$160.72	12.257%	$180.4195	$180.42	$180.40	$180.40
7 purchase totals =	$868.51		$950.5320	$950.53	$950.50	$950.50