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	$127.43	3.289%	$131.6212	$131.62	$131.60	$131.60
Purchase #2	$22.95	6.485%	$24.4383	$24.44	$24.45	$24.40
Purchase #3	$242.89	11.699%	$271.3057	$271.31	$271.30	$271.30
Purchase #4	$64.98	12.165%	$72.8848	$72.88	$72.90	$72.90
Purchase #5	$51.42	7.368%	$55.2086	$55.21	$55.20	$55.20
Purchase #6	$39.45	6.165%	$41.8821	$41.88	$41.90	$41.90
Purchase #7	$94.34	9.550%	$103.3495	$103.35	$103.35	$103.30
7 purchase totals =	$643.46		$700.6902	$700.69	$700.70	$700.60