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	$39.31	8.814%	$42.7748	$42.77	$42.75	$42.80
Purchase #2	$237.80	12.282%	$267.0066	$267.01	$267.00	$267.00
Purchase #3	$209.32	6.215%	$222.3292	$222.33	$222.35	$222.30
Purchase #4	$86.31	11.300%	$96.063	$96.06	$96.05	$96.10
Purchase #5	$178.33	4.217%	$185.8502	$185.85	$185.85	$185.90
Purchase #6	$78.79	5.302%	$82.9674	$82.97	$82.95	$83.00
Purchase #7	$166.55	8.244%	$180.2804	$180.28	$180.30	$180.30
7 purchase totals =	$996.41		$1,077.2716	$1,077.27	$1,077.25	$1,077.40