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	$131.31	4.771%	$137.5748	$137.57	$137.55	$137.60
Purchase #2	$89.46	12.214%	$100.3866	$100.39	$100.40	$100.40
Purchase #3	$75.45	10.145%	$83.1044	$83.10	$83.10	$83.10
Purchase #4	$8.42	5.270%	$8.8637	$8.86	$8.85	$8.90
Purchase #5	$140.42	4.167%	$146.2713	$146.27	$146.25	$146.30
Purchase #6	$229.59	5.785%	$242.8718	$242.87	$242.85	$242.90
Purchase #7	$58.96	5.740%	$62.3443	$62.34	$62.35	$62.30
7 purchase totals =	$733.61		$781.4169	$781.40	$781.35	$781.50