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	$62.93	13.191%	$71.2311	$71.23	$71.25	$71.20
Purchase #2	$161.54	8.239%	$174.8493	$174.85	$174.85	$174.80
Purchase #3	$208.82	3.361%	$215.8384	$215.84	$215.85	$215.80
Purchase #4	$81.50	6.544%	$86.8334	$86.83	$86.85	$86.80
Purchase #5	$103.46	7.161%	$110.8688	$110.87	$110.85	$110.90
Purchase #6	$31.68	5.249%	$33.3429	$33.34	$33.35	$33.30
Purchase #7	$243.25	6.601%	$259.3069	$259.31	$259.30	$259.30
7 purchase totals =	$893.18		$952.2708	$952.27	$952.30	$952.10