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	$18.43	6.253%	$19.5824	$19.58	$19.60	$19.60
Purchase #2	$250.86	13.186%	$283.9384	$283.94	$283.95	$283.90
Purchase #3	$81.61	5.751%	$86.3034	$86.30	$86.30	$86.30
Purchase #4	$220.98	11.382%	$246.1319	$246.13	$246.15	$246.10
Purchase #5	$243.56	13.272%	$275.8853	$275.89	$275.90	$275.90
Purchase #6	$78.59	7.500%	$84.4843	$84.48	$84.50	$84.50
Purchase #7	$81.98	5.644%	$86.607	$86.61	$86.60	$86.60
7 purchase totals =	$976.01		$1,082.9327	$1,082.93	$1,083.00	$1,082.90