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	$137.41	3.861%	$142.7154	$142.72	$142.70	$142.70
Purchase #2	$236.79	11.637%	$264.3453	$264.35	$264.35	$264.30
Purchase #3	$168.32	7.841%	$181.518	$181.52	$181.50	$181.50
Purchase #4	$61.88	9.760%	$67.9195	$67.92	$67.90	$67.90
Purchase #5	$196.64	9.470%	$215.2618	$215.26	$215.25	$215.30
Purchase #6	$15.64	12.349%	$17.5714	$17.57	$17.55	$17.60
Purchase #7	$200.57	13.631%	$227.9097	$227.91	$227.90	$227.90
7 purchase totals =	$1,017.25		$1,117.2411	$1,117.25	$1,117.15	$1,117.20