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	$14.52	5.759%	$15.3562	$15.36	$15.35	$15.40
Purchase #2	$65.59	7.308%	$70.3833	$70.38	$70.40	$70.40
Purchase #3	$82.46	10.652%	$91.2436	$91.24	$91.25	$91.20
Purchase #4	$95.75	3.225%	$98.8379	$98.84	$98.85	$98.80
Purchase #5	$173.57	7.348%	$186.3239	$186.32	$186.30	$186.30
Purchase #6	$239.30	10.529%	$264.4959	$264.50	$264.50	$264.50
Purchase #7	$191.82	12.336%	$215.4829	$215.48	$215.50	$215.50
7 purchase totals =	$863.01		$942.1237	$942.12	$942.15	$942.10