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	$126.96	12.152%	$142.3882	$142.39	$142.40	$142.40
Purchase #2	$211.63	5.795%	$223.894	$223.89	$223.90	$223.90
Purchase #3	$6.66	11.273%	$7.4108	$7.41	$7.40	$7.40
Purchase #4	$81.76	10.473%	$90.3227	$90.32	$90.30	$90.30
Purchase #5	$23.64	11.480%	$26.3539	$26.35	$26.35	$26.40
Purchase #6	$225.56	5.421%	$237.7876	$237.79	$237.80	$237.80
Purchase #7	$45.48	6.227%	$48.312	$48.31	$48.30	$48.30
7 purchase totals =	$721.69		$776.4692	$776.46	$776.45	$776.50