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	$178.90	6.138%	$189.8809	$189.88	$189.90	$189.90
Purchase #2	$66.26	8.446%	$71.8563	$71.86	$71.85	$71.90
Purchase #3	$166.87	12.637%	$187.9574	$187.96	$187.95	$188.00
Purchase #4	$79.48	3.565%	$82.3135	$82.31	$82.30	$82.30
Purchase #5	$52.82	10.788%	$58.5182	$58.52	$58.50	$58.50
Purchase #6	$91.61	8.327%	$99.2384	$99.24	$99.25	$99.20
Purchase #7	$89.89	6.214%	$95.4758	$95.48	$95.50	$95.50
7 purchase totals =	$725.83		$785.2405	$785.25	$785.25	$785.30