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	$203.58	3.306%	$210.3104	$210.31	$210.30	$210.30
Purchase #2	$30.79	7.704%	$33.1621	$33.16	$33.15	$33.20
Purchase #3	$33.90	4.716%	$35.4987	$35.50	$35.50	$35.50
Purchase #4	$129.36	7.703%	$139.3246	$139.32	$139.30	$139.30
Purchase #5	$93.34	10.820%	$103.4394	$103.44	$103.45	$103.40
Purchase #6	$151.93	12.720%	$171.2555	$171.26	$171.25	$171.30
Purchase #7	$245.69	13.711%	$279.3766	$279.38	$279.40	$279.40
7 purchase totals =	$888.59		$972.3673	$972.37	$972.35	$972.40