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	$86.61	4.311%	$90.3438	$90.34	$90.35	$90.30
Purchase #2	$78.88	13.792%	$89.7591	$89.76	$89.75	$89.80
Purchase #3	$99.33	7.833%	$107.1105	$107.11	$107.10	$107.10
Purchase #4	$88.92	5.723%	$94.0089	$94.01	$94.00	$94.00
Purchase #5	$5.34	12.800%	$6.0235	$6.02	$6.00	$6.00
Purchase #6	$166.55	7.853%	$179.6292	$179.63	$179.65	$179.60
Purchase #7	$133.96	3.274%	$138.3459	$138.35	$138.35	$138.30
7 purchase totals =	$659.59		$705.2209	$705.22	$705.20	$705.10