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	$135.98	6.281%	$144.5209	$144.52	$144.50	$144.50
Purchase #2	$216.54	12.508%	$243.6248	$243.62	$243.60	$243.60
Purchase #3	$120.71	9.231%	$131.8527	$131.85	$131.85	$131.90
Purchase #4	$81.94	5.569%	$86.5032	$86.50	$86.50	$86.50
Purchase #5	$190.41	4.632%	$199.2298	$199.23	$199.25	$199.20
Purchase #6	$7.59	4.710%	$7.9475	$7.95	$7.95	$7.90
Purchase #7	$185.32	11.791%	$207.1711	$207.17	$207.15	$207.20
7 purchase totals =	$938.49		$1,020.8500	$1,020.84	$1,020.80	$1,020.80