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	$75.96	3.729%	$78.7925	$78.79	$78.80	$78.80
Purchase #2	$206.51	7.293%	$221.5708	$221.57	$221.55	$221.60
Purchase #3	$245.43	8.860%	$267.1751	$267.18	$267.20	$267.20
Purchase #4	$211.76	6.839%	$226.2423	$226.24	$226.25	$226.20
Purchase #5	$58.40	11.850%	$65.3204	$65.32	$65.30	$65.30
Purchase #6	$57.88	12.815%	$65.2973	$65.30	$65.30	$65.30
Purchase #7	$167.65	6.629%	$178.7635	$178.76	$178.75	$178.80
7 purchase totals =	$1,023.59		$1,103.1619	$1,103.16	$1,103.15	$1,103.20