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	$104.91	6.582%	$111.8152	$111.82	$111.80	$111.80
Purchase #2	$165.41	12.128%	$185.4709	$185.47	$185.45	$185.50
Purchase #3	$195.46	4.424%	$204.1072	$204.11	$204.10	$204.10
Purchase #4	$218.54	11.199%	$243.0143	$243.01	$243.00	$243.00
Purchase #5	$185.45	5.577%	$195.7925	$195.79	$195.80	$195.80
Purchase #6	$101.96	7.109%	$109.2083	$109.21	$109.20	$109.20
Purchase #7	$83.47	9.490%	$91.3913	$91.39	$91.40	$91.40
7 purchase totals =	$1,055.20		$1,140.7997	$1,140.80	$1,140.75	$1,140.80