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	$190.78	13.790%	$217.0886	$217.09	$217.10	$217.10
Purchase #2	$137.57	6.359%	$146.3181	$146.32	$146.30	$146.30
Purchase #3	$220.56	13.113%	$249.482	$249.48	$249.50	$249.50
Purchase #4	$105.83	4.687%	$110.7903	$110.79	$110.80	$110.80
Purchase #5	$92.52	7.380%	$99.348	$99.35	$99.35	$99.30
Purchase #6	$180.52	5.874%	$191.1237	$191.12	$191.10	$191.10
Purchase #7	$82.48	4.399%	$86.1083	$86.11	$86.10	$86.10
7 purchase totals =	$1,010.26		$1,100.2590	$1,100.26	$1,100.25	$1,100.20