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	$90.77	6.380%	$96.5611	$96.56	$96.55	$96.60
Purchase #2	$191.72	9.155%	$209.272	$209.27	$209.25	$209.30
Purchase #3	$161.61	6.145%	$171.5409	$171.54	$171.55	$171.50
Purchase #4	$214.46	5.326%	$225.8821	$225.88	$225.90	$225.90
Purchase #5	$248.70	10.454%	$274.6991	$274.70	$274.70	$274.70
Purchase #6	$13.31	9.367%	$14.5567	$14.56	$14.55	$14.60
Purchase #7	$20.52	9.711%	$22.5127	$22.51	$22.50	$22.50
7 purchase totals =	$941.09		$1,015.0246	$1,015.02	$1,015.00	$1,015.10