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	$91.71	11.347%	$102.1163	$102.12	$102.10	$102.10
Purchase #2	$95.76	8.281%	$103.6899	$103.69	$103.70	$103.70
Purchase #3	$201.92	4.412%	$210.8287	$210.83	$210.85	$210.80
Purchase #4	$182.28	7.719%	$196.3502	$196.35	$196.35	$196.40
Purchase #5	$78.30	3.144%	$80.7618	$80.76	$80.75	$80.80
Purchase #6	$136.34	4.281%	$142.1767	$142.18	$142.20	$142.20
Purchase #7	$93.86	10.319%	$103.5454	$103.55	$103.55	$103.50
7 purchase totals =	$880.17		$939.4690	$939.48	$939.50	$939.50