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	$8.32	4.354%	$8.6823	$8.68	$8.70	$8.70
Purchase #2	$212.56	3.254%	$219.4767	$219.48	$219.50	$219.50
Purchase #3	$149.86	8.144%	$162.0646	$162.06	$162.05	$162.10
Purchase #4	$31.98	10.446%	$35.3206	$35.32	$35.30	$35.30
Purchase #5	$82.64	8.649%	$89.7875	$89.79	$89.80	$89.80
Purchase #6	$76.77	12.342%	$86.245	$86.25	$86.25	$86.20
Purchase #7	$166.57	12.234%	$186.9482	$186.95	$186.95	$186.90
7 purchase totals =	$728.70		$788.5249	$788.53	$788.55	$788.50