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	$80.26	12.480%	$90.2764	$90.28	$90.30	$90.30
Purchase #2	$100.63	8.365%	$109.0477	$109.05	$109.05	$109.00
Purchase #3	$46.25	11.107%	$51.387	$51.39	$51.40	$51.40
Purchase #4	$221.46	11.425%	$246.7618	$246.76	$246.75	$246.80
Purchase #5	$115.47	7.526%	$124.1603	$124.16	$124.15	$124.20
Purchase #6	$42.91	11.618%	$47.8953	$47.90	$47.90	$47.90
Purchase #7	$249.87	12.600%	$281.3536	$281.35	$281.35	$281.40
7 purchase totals =	$856.85		$950.8821	$950.89	$950.90	$951.00