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	$101.33	11.432%	$112.914	$112.91	$112.90	$112.90
Purchase #2	$36.90	12.524%	$41.5214	$41.52	$41.50	$41.50
Purchase #3	$218.35	9.590%	$239.2898	$239.29	$239.30	$239.30
Purchase #4	$167.74	12.775%	$189.1688	$189.17	$189.15	$189.20
Purchase #5	$136.56	3.854%	$141.823	$141.82	$141.80	$141.80
Purchase #6	$89.43	12.148%	$100.294	$100.29	$100.30	$100.30
Purchase #7	$66.28	12.308%	$74.4377	$74.44	$74.45	$74.40
7 purchase totals =	$816.59		$899.4487	$899.44	$899.40	$899.40