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	$100.51	4.354%	$104.8862	$104.89	$104.90	$104.90
Purchase #2	$166.90	11.336%	$185.8198	$185.82	$185.80	$185.80
Purchase #3	$149.55	10.729%	$165.5952	$165.60	$165.60	$165.60
Purchase #4	$212.50	13.190%	$240.5288	$240.53	$240.55	$240.50
Purchase #5	$197.36	3.549%	$204.3643	$204.36	$204.35	$204.40
Purchase #6	$44.47	7.383%	$47.7532	$47.75	$47.75	$47.80
Purchase #7	$131.90	7.142%	$141.3203	$141.32	$141.30	$141.30
7 purchase totals =	$1,003.19		$1,090.2678	$1,090.27	$1,090.25	$1,090.30