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	$91.77	7.781%	$98.9106	$98.91	$98.90	$98.90
Purchase #2	$71.36	11.468%	$79.5436	$79.54	$79.55	$79.50
Purchase #3	$80.42	3.427%	$83.176	$83.18	$83.20	$83.20
Purchase #4	$44.98	8.766%	$48.9229	$48.92	$48.90	$48.90
Purchase #5	$195.92	10.141%	$215.7882	$215.79	$215.80	$215.80
Purchase #6	$55.29	11.496%	$61.6461	$61.65	$61.65	$61.60
Purchase #7	$119.68	3.535%	$123.9107	$123.91	$123.90	$123.90
7 purchase totals =	$659.42		$711.8981	$711.90	$711.90	$711.80