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	$240.32	12.481%	$270.3143	$270.31	$270.30	$270.30
Purchase #2	$216.56	4.260%	$225.7855	$225.79	$225.80	$225.80
Purchase #3	$131.56	6.294%	$139.8404	$139.84	$139.85	$139.80
Purchase #4	$90.90	9.605%	$99.6309	$99.63	$99.65	$99.60
Purchase #5	$61.91	6.368%	$65.8524	$65.85	$65.85	$65.90
Purchase #6	$110.33	8.276%	$119.4609	$119.46	$119.45	$119.50
Purchase #7	$150.49	6.582%	$160.3953	$160.40	$160.40	$160.40
7 purchase totals =	$1,002.07		$1,081.2797	$1,081.28	$1,081.30	$1,081.30