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	$159.54	3.300%	$164.8048	$164.80	$164.80	$164.80
Purchase #2	$45.57	3.471%	$47.1517	$47.15	$47.15	$47.20
Purchase #3	$145.91	3.597%	$151.1584	$151.16	$151.15	$151.20
Purchase #4	$171.76	6.425%	$182.7956	$182.80	$182.80	$182.80
Purchase #5	$48.61	10.590%	$53.7578	$53.76	$53.75	$53.80
Purchase #6	$217.32	3.570%	$225.0783	$225.08	$225.10	$225.10
Purchase #7	$161.88	4.209%	$168.6935	$168.69	$168.70	$168.70
7 purchase totals =	$950.59		$993.4401	$993.44	$993.45	$993.60