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	$128.88	13.521%	$146.3059	$146.31	$146.30	$146.30
Purchase #2	$38.77	7.627%	$41.727	$41.73	$41.75	$41.70
Purchase #3	$166.37	4.620%	$174.0563	$174.06	$174.05	$174.10
Purchase #4	$36.57	11.804%	$40.8867	$40.89	$40.90	$40.90
Purchase #5	$194.60	12.393%	$218.7168	$218.72	$218.70	$218.70
Purchase #6	$126.69	3.725%	$131.4092	$131.41	$131.40	$131.40
Purchase #7	$78.59	3.357%	$81.2283	$81.23	$81.25	$81.20
7 purchase totals =	$770.47		$834.3302	$834.35	$834.35	$834.30