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	$230.96	8.654%	$250.9473	$250.95	$250.95	$250.90
Purchase #2	$115.36	4.298%	$120.3182	$120.32	$120.30	$120.30
Purchase #3	$193.32	13.727%	$219.857	$219.86	$219.85	$219.90
Purchase #4	$28.74	8.368%	$31.145	$31.15	$31.15	$31.10
Purchase #5	$44.44	3.287%	$45.9007	$45.90	$45.90	$45.90
Purchase #6	$132.61	13.483%	$150.4898	$150.49	$150.50	$150.50
Purchase #7	$215.67	7.298%	$231.4096	$231.41	$231.40	$231.40
7 purchase totals =	$961.10		$1,050.0676	$1,050.08	$1,050.05	$1,050.00