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	$6.83	3.750%	$7.0861	$7.09	$7.10	$7.10
Purchase #2	$40.57	7.700%	$43.6939	$43.69	$43.70	$43.70
Purchase #3	$44.36	9.851%	$48.7299	$48.73	$48.75	$48.70
Purchase #4	$181.70	8.360%	$196.8901	$196.89	$196.90	$196.90
Purchase #5	$56.82	9.571%	$62.2582	$62.26	$62.25	$62.30
Purchase #6	$7.89	5.377%	$8.3142	$8.31	$8.30	$8.30
Purchase #7	$104.67	3.412%	$108.2413	$108.24	$108.25	$108.20
7 purchase totals =	$442.84		$475.2137	$475.21	$475.25	$475.20