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	$143.55	12.104%	$160.9253	$160.93	$160.95	$160.90
Purchase #2	$73.40	7.501%	$78.9057	$78.91	$78.90	$78.90
Purchase #3	$236.31	4.762%	$247.5631	$247.56	$247.55	$247.60
Purchase #4	$169.50	9.133%	$184.9804	$184.98	$185.00	$185.00
Purchase #5	$213.35	7.117%	$228.5341	$228.53	$228.55	$228.50
Purchase #6	$249.44	3.407%	$257.9384	$257.94	$257.95	$257.90
Purchase #7	$137.99	3.179%	$142.3767	$142.38	$142.40	$142.40
7 purchase totals =	$1,223.54		$1,301.2237	$1,301.23	$1,301.30	$1,301.20