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	$65.91	8.423%	$71.4616	$71.46	$71.45	$71.50
Purchase #2	$232.95	7.735%	$250.9687	$250.97	$250.95	$251.00
Purchase #3	$79.84	12.301%	$89.6611	$89.66	$89.65	$89.70
Purchase #4	$150.84	6.301%	$160.3444	$160.34	$160.35	$160.30
Purchase #5	$69.40	12.873%	$78.3339	$78.33	$78.35	$78.30
Purchase #6	$64.69	11.129%	$71.8894	$71.89	$71.90	$71.90
Purchase #7	$97.70	11.646%	$109.0781	$109.08	$109.10	$109.10
7 purchase totals =	$761.33		$831.7372	$831.73	$831.75	$831.80