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	$69.80	10.743%	$77.2986	$77.30	$77.30	$77.30
Purchase #2	$75.54	3.684%	$78.3229	$78.32	$78.30	$78.30
Purchase #3	$208.31	5.401%	$219.5608	$219.56	$219.55	$219.60
Purchase #4	$204.94	9.260%	$223.9174	$223.92	$223.90	$223.90
Purchase #5	$139.35	5.791%	$147.4198	$147.42	$147.40	$147.40
Purchase #6	$72.38	11.424%	$80.6487	$80.65	$80.65	$80.60
Purchase #7	$247.49	13.612%	$281.1783	$281.18	$281.20	$281.20
7 purchase totals =	$1,017.81		$1,108.3465	$1,108.35	$1,108.30	$1,108.30