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	$130.60	9.399%	$142.8751	$142.88	$142.90	$142.90
Purchase #2	$26.86	5.310%	$28.2863	$28.29	$28.30	$28.30
Purchase #3	$239.81	10.293%	$264.4936	$264.49	$264.50	$264.50
Purchase #4	$135.56	12.498%	$152.5023	$152.50	$152.50	$152.50
Purchase #5	$137.66	6.486%	$146.5886	$146.59	$146.60	$146.60
Purchase #6	$125.44	6.782%	$133.9473	$133.95	$133.95	$133.90
Purchase #7	$53.96	9.838%	$59.2686	$59.27	$59.25	$59.30
7 purchase totals =	$849.89		$927.9618	$927.97	$928.00	$928.00