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	$87.89	12.330%	$98.7268	$98.73	$98.75	$98.70
Purchase #2	$164.84	10.253%	$181.741	$181.74	$181.75	$181.70
Purchase #3	$250.44	4.318%	$261.254	$261.25	$261.25	$261.30
Purchase #4	$157.59	4.427%	$164.5665	$164.57	$164.55	$164.60
Purchase #5	$122.44	13.663%	$139.169	$139.17	$139.15	$139.20
Purchase #6	$140.41	8.805%	$152.7731	$152.77	$152.75	$152.80
Purchase #7	$170.28	11.862%	$190.4786	$190.48	$190.50	$190.50
7 purchase totals =	$1,093.89		$1,188.7090	$1,188.71	$1,188.70	$1,188.80