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	$115.84	13.550%	$131.5363	$131.54	$131.55	$131.50
Purchase #2	$26.30	3.529%	$27.2281	$27.23	$27.25	$27.20
Purchase #3	$202.77	4.786%	$212.4746	$212.47	$212.45	$212.50
Purchase #4	$179.71	5.713%	$189.9768	$189.98	$190.00	$190.00
Purchase #5	$124.69	7.645%	$134.2226	$134.22	$134.20	$134.20
Purchase #6	$160.82	11.569%	$179.4253	$179.43	$179.45	$179.40
Purchase #7	$195.85	12.119%	$219.5851	$219.59	$219.60	$219.60
7 purchase totals =	$1,005.98		$1,094.4488	$1,094.46	$1,094.50	$1,094.40