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	$164.51	6.299%	$174.8725	$174.87	$174.85	$174.90
Purchase #2	$60.79	12.788%	$68.5638	$68.56	$68.55	$68.60
Purchase #3	$88.51	11.860%	$99.0073	$99.01	$99.00	$99.00
Purchase #4	$81.44	7.456%	$87.5122	$87.51	$87.50	$87.50
Purchase #5	$53.70	11.282%	$59.7584	$59.76	$59.75	$59.80
Purchase #6	$231.54	6.421%	$246.4072	$246.41	$246.40	$246.40
Purchase #7	$40.29	8.700%	$43.7952	$43.80	$43.80	$43.80
7 purchase totals =	$720.78		$779.9166	$779.92	$779.85	$780.00