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	$77.45	4.829%	$81.1901	$81.19	$81.20	$81.20
Purchase #2	$219.51	10.222%	$241.9483	$241.95	$241.95	$241.90
Purchase #3	$67.82	13.123%	$76.72	$76.72	$76.70	$76.70
Purchase #4	$234.85	4.349%	$245.0636	$245.06	$245.05	$245.10
Purchase #5	$174.27	10.686%	$192.8925	$192.89	$192.90	$192.90
Purchase #6	$47.36	11.671%	$52.8874	$52.89	$52.90	$52.90
Purchase #7	$245.70	7.616%	$264.4125	$264.41	$264.40	$264.40
7 purchase totals =	$1,066.96		$1,155.1144	$1,155.11	$1,155.10	$1,155.10