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	$39.82	5.778%	$42.1208	$42.12	$42.10	$42.10
Purchase #2	$154.71	6.218%	$164.3299	$164.33	$164.35	$164.30
Purchase #3	$200.30	9.774%	$219.8773	$219.88	$219.90	$219.90
Purchase #4	$179.35	6.109%	$190.3065	$190.31	$190.30	$190.30
Purchase #5	$142.75	5.244%	$150.2358	$150.24	$150.25	$150.20
Purchase #6	$138.63	6.372%	$147.4635	$147.46	$147.45	$147.50
Purchase #7	$218.95	6.492%	$233.1642	$233.16	$233.15	$233.20
7 purchase totals =	$1,074.51		$1,147.4980	$1,147.50	$1,147.50	$1,147.50