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	$98.53	13.336%	$111.67	$111.67	$111.65	$111.70
Purchase #2	$115.86	4.119%	$120.6323	$120.63	$120.65	$120.60
Purchase #3	$18.48	11.274%	$20.5634	$20.56	$20.55	$20.60
Purchase #4	$195.32	12.854%	$220.4264	$220.43	$220.45	$220.40
Purchase #5	$159.96	11.803%	$178.8401	$178.84	$178.85	$178.80
Purchase #6	$110.53	13.223%	$125.1454	$125.15	$125.15	$125.10
Purchase #7	$145.59	12.666%	$164.0304	$164.03	$164.05	$164.00
7 purchase totals =	$844.27		$941.3080	$941.31	$941.35	$941.20