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	$199.42	11.332%	$222.0183	$222.02	$222.00	$222.00
Purchase #2	$225.63	13.570%	$256.248	$256.25	$256.25	$256.20
Purchase #3	$80.78	12.547%	$90.9155	$90.92	$90.90	$90.90
Purchase #4	$160.40	12.375%	$180.2495	$180.25	$180.25	$180.20
Purchase #5	$145.92	9.655%	$160.0086	$160.01	$160.00	$160.00
Purchase #6	$9.25	11.167%	$10.2829	$10.28	$10.30	$10.30
Purchase #7	$31.96	4.506%	$33.4001	$33.40	$33.40	$33.40
7 purchase totals =	$853.36		$953.1229	$953.13	$953.10	$953.00