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	$45.59	12.355%	$51.2226	$51.22	$51.20	$51.20
Purchase #2	$150.46	12.558%	$169.3548	$169.35	$169.35	$169.40
Purchase #3	$37.69	8.553%	$40.9136	$40.91	$40.90	$40.90
Purchase #4	$206.26	6.110%	$218.8625	$218.86	$218.85	$218.90
Purchase #5	$67.34	5.469%	$71.0228	$71.02	$71.00	$71.00
Purchase #6	$236.54	8.577%	$256.828	$256.83	$256.85	$256.80
Purchase #7	$242.78	8.212%	$262.7171	$262.72	$262.70	$262.70
7 purchase totals =	$986.66		$1,070.9214	$1,070.91	$1,070.85	$1,070.90