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	$32.44	4.163%	$33.7905	$33.79	$33.80	$33.80
Purchase #2	$245.36	13.386%	$278.2039	$278.20	$278.20	$278.20
Purchase #3	$34.65	9.298%	$37.8718	$37.87	$37.85	$37.90
Purchase #4	$92.46	12.238%	$103.7753	$103.78	$103.80	$103.80
Purchase #5	$166.89	11.595%	$186.2409	$186.24	$186.25	$186.20
Purchase #6	$81.56	11.376%	$90.8383	$90.84	$90.85	$90.80
Purchase #7	$17.69	12.421%	$19.8873	$19.89	$19.90	$19.90
7 purchase totals =	$671.05		$750.6080	$750.61	$750.65	$750.60