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	$131.73	4.801%	$138.0544	$138.05	$138.05	$138.10
Purchase #2	$175.96	7.611%	$189.3523	$189.35	$189.35	$189.40
Purchase #3	$111.45	13.362%	$126.3419	$126.34	$126.35	$126.30
Purchase #4	$227.48	3.841%	$236.2175	$236.22	$236.20	$236.20
Purchase #5	$57.28	9.614%	$62.7869	$62.79	$62.80	$62.80
Purchase #6	$217.36	6.512%	$231.5145	$231.51	$231.50	$231.50
Purchase #7	$190.29	3.285%	$196.541	$196.54	$196.55	$196.50
7 purchase totals =	$1,111.55		$1,180.8085	$1,180.80	$1,180.80	$1,180.80