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	$92.49	12.359%	$103.9208	$103.92	$103.90	$103.90
Purchase #2	$179.70	6.692%	$191.7255	$191.73	$191.75	$191.70
Purchase #3	$48.79	4.506%	$50.9885	$50.99	$51.00	$51.00
Purchase #4	$5.57	4.552%	$5.8235	$5.82	$5.80	$5.80
Purchase #5	$249.35	3.800%	$258.8253	$258.83	$258.85	$258.80
Purchase #6	$126.82	11.220%	$141.0492	$141.05	$141.05	$141.00
Purchase #7	$123.61	13.171%	$139.8907	$139.89	$139.90	$139.90
7 purchase totals =	$826.33		$892.2235	$892.23	$892.25	$892.10