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	$70.55	12.183%	$79.1451	$79.15	$79.15	$79.10
Purchase #2	$205.46	5.293%	$216.335	$216.34	$216.35	$216.30
Purchase #3	$73.32	12.776%	$82.6874	$82.69	$82.70	$82.70
Purchase #4	$173.59	6.682%	$185.1893	$185.19	$185.20	$185.20
Purchase #5	$37.86	12.443%	$42.5709	$42.57	$42.55	$42.60
Purchase #6	$249.79	7.631%	$268.8515	$268.85	$268.85	$268.90
Purchase #7	$38.59	11.690%	$43.1012	$43.10	$43.10	$43.10
7 purchase totals =	$849.16		$917.8804	$917.89	$917.90	$917.90