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	$91.34	8.642%	$99.2336	$99.23	$99.25	$99.20
Purchase #2	$239.74	12.781%	$270.3812	$270.38	$270.40	$270.40
Purchase #3	$150.36	8.142%	$162.6023	$162.60	$162.60	$162.60
Purchase #4	$121.59	12.448%	$136.7255	$136.73	$136.75	$136.70
Purchase #5	$221.72	3.638%	$229.7862	$229.79	$229.80	$229.80
Purchase #6	$193.59	8.343%	$209.7412	$209.74	$209.75	$209.70
Purchase #7	$13.72	6.254%	$14.578	$14.58	$14.60	$14.60
7 purchase totals =	$1,032.06		$1,123.0480	$1,123.05	$1,123.15	$1,123.00