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	$30.54	9.576%	$33.4645	$33.46	$33.45	$33.50
Purchase #2	$241.68	3.401%	$249.8995	$249.90	$249.90	$249.90
Purchase #3	$29.53	12.681%	$33.2747	$33.27	$33.25	$33.30
Purchase #4	$8.46	3.817%	$8.7829	$8.78	$8.80	$8.80
Purchase #5	$175.64	13.204%	$198.8315	$198.83	$198.85	$198.80
Purchase #6	$165.47	3.510%	$171.278	$171.28	$171.30	$171.30
Purchase #7	$218.27	11.401%	$243.155	$243.16	$243.15	$243.20
7 purchase totals =	$869.59		$938.6861	$938.68	$938.70	$938.80