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	$189.38	12.216%	$212.5147	$212.51	$212.50	$212.50
Purchase #2	$155.98	11.833%	$174.4371	$174.44	$174.45	$174.40
Purchase #3	$155.80	5.790%	$164.8208	$164.82	$164.80	$164.80
Purchase #4	$101.44	3.692%	$105.1852	$105.19	$105.20	$105.20
Purchase #5	$75.86	8.393%	$82.2269	$82.23	$82.25	$82.20
Purchase #6	$159.53	3.148%	$164.552	$164.55	$164.55	$164.60
Purchase #7	$86.46	4.140%	$90.0394	$90.04	$90.05	$90.00
7 purchase totals =	$924.45		$993.7761	$993.78	$993.80	$993.70