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	$182.92	3.774%	$189.8234	$189.82	$189.80	$189.80
Purchase #2	$221.90	7.416%	$238.3561	$238.36	$238.35	$238.40
Purchase #3	$97.79	6.296%	$103.9469	$103.95	$103.95	$103.90
Purchase #4	$139.76	7.713%	$150.5397	$150.54	$150.55	$150.50
Purchase #5	$29.96	4.508%	$31.3106	$31.31	$31.30	$31.30
Purchase #6	$79.46	5.199%	$83.5911	$83.59	$83.60	$83.60
Purchase #7	$193.32	13.568%	$219.5497	$219.55	$219.55	$219.50
7 purchase totals =	$945.11		$1,017.1175	$1,017.12	$1,017.10	$1,017.00