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	$5.57	13.387%	$6.3157	$6.32	$6.30	$6.30
Purchase #2	$90.77	12.830%	$102.4158	$102.42	$102.40	$102.40
Purchase #3	$246.70	7.371%	$264.8843	$264.88	$264.90	$264.90
Purchase #4	$66.78	8.199%	$72.2553	$72.26	$72.25	$72.30
Purchase #5	$179.59	11.505%	$200.2518	$200.25	$200.25	$200.30
Purchase #6	$246.69	6.181%	$261.9379	$261.94	$261.95	$261.90
Purchase #7	$145.55	3.376%	$150.4638	$150.46	$150.45	$150.50
7 purchase totals =	$981.65		$1,058.5246	$1,058.53	$1,058.50	$1,058.60