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	$170.33	5.288%	$179.3371	$179.34	$179.35	$179.30
Purchase #2	$41.26	9.190%	$45.0518	$45.05	$45.05	$45.10
Purchase #3	$101.66	5.261%	$107.0083	$107.01	$107.00	$107.00
Purchase #4	$40.83	5.192%	$42.9499	$42.95	$42.95	$42.90
Purchase #5	$245.57	7.471%	$263.9165	$263.92	$263.90	$263.90
Purchase #6	$209.93	6.358%	$223.2773	$223.28	$223.30	$223.30
Purchase #7	$130.85	12.778%	$147.57	$147.57	$147.55	$147.60
7 purchase totals =	$940.43		$1,009.1109	$1,009.12	$1,009.10	$1,009.10