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	$7.42	4.719%	$7.7701	$7.77	$7.75	$7.80
Purchase #2	$86.89	7.416%	$93.3338	$93.33	$93.35	$93.30
Purchase #3	$78.48	13.456%	$89.0403	$89.04	$89.05	$89.00
Purchase #4	$142.44	9.668%	$156.2111	$156.21	$156.20	$156.20
Purchase #5	$9.39	8.654%	$10.2026	$10.20	$10.20	$10.20
Purchase #6	$203.28	10.516%	$224.6569	$224.66	$224.65	$224.70
Purchase #7	$81.56	5.825%	$86.3109	$86.31	$86.30	$86.30
7 purchase totals =	$609.46		$667.5257	$667.52	$667.50	$667.50