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	$130.51	4.126%	$135.8948	$135.89	$135.90	$135.90
Purchase #2	$139.35	5.476%	$146.9808	$146.98	$147.00	$147.00
Purchase #3	$99.68	4.208%	$103.8745	$103.87	$103.85	$103.90
Purchase #4	$31.79	4.583%	$33.2469	$33.25	$33.25	$33.20
Purchase #5	$248.27	8.442%	$269.229	$269.23	$269.25	$269.20
Purchase #6	$73.53	12.582%	$82.7815	$82.78	$82.80	$82.80
Purchase #7	$104.99	9.407%	$114.8664	$114.87	$114.85	$114.90
7 purchase totals =	$828.12		$886.8739	$886.87	$886.90	$886.90