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	$99.61	6.735%	$106.3187	$106.32	$106.30	$106.30
Purchase #2	$144.35	13.835%	$164.3208	$164.32	$164.30	$164.30
Purchase #3	$92.67	6.807%	$98.978	$98.98	$99.00	$99.00
Purchase #4	$77.83	8.492%	$84.4393	$84.44	$84.45	$84.40
Purchase #5	$80.31	6.244%	$85.3246	$85.32	$85.30	$85.30
Purchase #6	$57.64	10.402%	$63.6357	$63.64	$63.65	$63.60
Purchase #7	$164.80	12.654%	$185.6538	$185.65	$185.65	$185.70
7 purchase totals =	$717.21		$788.6709	$788.67	$788.65	$788.60