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	$166.65	6.633%	$177.7039	$177.70	$177.70	$177.70
Purchase #2	$54.86	8.592%	$59.5736	$59.57	$59.55	$59.60
Purchase #3	$70.43	4.183%	$73.3761	$73.38	$73.40	$73.40
Purchase #4	$83.43	4.139%	$86.8832	$86.88	$86.90	$86.90
Purchase #5	$91.46	5.371%	$96.3723	$96.37	$96.35	$96.40
Purchase #6	$231.59	5.837%	$245.1079	$245.11	$245.10	$245.10
Purchase #7	$67.31	6.158%	$71.4549	$71.45	$71.45	$71.50
7 purchase totals =	$765.73		$810.4719	$810.46	$810.45	$810.60