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	$98.25	5.742%	$103.8915	$103.89	$103.90	$103.90
Purchase #2	$209.39	6.667%	$223.35	$223.35	$223.35	$223.40
Purchase #3	$72.33	8.767%	$78.6712	$78.67	$78.65	$78.70
Purchase #4	$171.28	10.221%	$188.7865	$188.79	$188.80	$188.80
Purchase #5	$210.38	12.266%	$236.1852	$236.19	$236.20	$236.20
Purchase #6	$78.65	6.221%	$83.5428	$83.54	$83.55	$83.50
Purchase #7	$56.49	11.226%	$62.8316	$62.83	$62.85	$62.80
7 purchase totals =	$896.77		$977.2588	$977.26	$977.30	$977.30