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	$90.44	5.728%	$95.6204	$95.62	$95.60	$95.60
Purchase #2	$102.37	10.713%	$113.3369	$113.34	$113.35	$113.30
Purchase #3	$125.89	8.744%	$136.8978	$136.90	$136.90	$136.90
Purchase #4	$104.36	5.692%	$110.3002	$110.30	$110.30	$110.30
Purchase #5	$141.74	6.380%	$150.783	$150.78	$150.80	$150.80
Purchase #6	$83.49	8.208%	$90.3429	$90.34	$90.35	$90.30
Purchase #7	$141.63	13.162%	$160.2713	$160.27	$160.25	$160.30
7 purchase totals =	$789.92		$857.5525	$857.55	$857.55	$857.50