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	$229.62	4.704%	$240.4213	$240.42	$240.40	$240.40
Purchase #2	$85.25	8.406%	$92.4161	$92.42	$92.40	$92.40
Purchase #3	$6.34	5.328%	$6.6778	$6.68	$6.70	$6.70
Purchase #4	$235.90	4.871%	$247.3907	$247.39	$247.40	$247.40
Purchase #5	$250.31	7.631%	$269.4112	$269.41	$269.40	$269.40
Purchase #6	$139.97	8.835%	$152.3363	$152.34	$152.35	$152.30
Purchase #7	$72.91	7.137%	$78.1136	$78.11	$78.10	$78.10
7 purchase totals =	$1,020.30		$1,086.7670	$1,086.77	$1,086.75	$1,086.70