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	$104.50	3.557%	$108.2171	$108.22	$108.20	$108.20
Purchase #2	$169.59	11.542%	$189.1641	$189.16	$189.15	$189.20
Purchase #3	$163.34	4.818%	$171.2097	$171.21	$171.20	$171.20
Purchase #4	$169.91	11.152%	$188.8584	$188.86	$188.85	$188.90
Purchase #5	$64.98	12.188%	$72.8998	$72.90	$72.90	$72.90
Purchase #6	$79.59	5.409%	$83.895	$83.90	$83.90	$83.90
Purchase #7	$156.60	7.329%	$168.0772	$168.08	$168.10	$168.10
7 purchase totals =	$908.51		$982.3213	$982.33	$982.30	$982.40